ggml : suppress double-promotion warning in GGML_F16x4_REDUCE

This commit adds a cast to `ggml_float` in the `GGML_F16x4_REDUCE` macro
to suppress a double-promotion warning.

Currently the following warning is generated when compiling the
command.wasm example:
```console
/whisper-work/ggml/src/ggml-cpu/ggml-cpu.c:1592:5: warning: implicit conversion increases floating-point precision: 'float' to 'ggml_float' (aka 'double') [-Wdouble-promotion]
 1592 |     GGML_F16_VEC_REDUCE(sumf, sum);
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Users/danbev/work/ai/whisper-work/ggml/src/ggml-cpu/ggml-cpu.c:932:37: note: expanded from macro 'GGML_F16_VEC_REDUCE'
  932 | #define GGML_F16_VEC_REDUCE         GGML_F16x4_REDUCE
      |                                     ^
/Users/danbev/work/ai/whisper-work/ggml/src/ggml-cpu/ggml-cpu.c:920:44: note: expanded from macro 'GGML_F16x4_REDUCE'
  918 |     res = wasm_f32x4_extract_lane(x[0], 0) +       \
      |         ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  919 |           wasm_f32x4_extract_lane(x[0], 1) +       \
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  920 |           wasm_f32x4_extract_lane(x[0], 2) +       \
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~
  921 |           wasm_f32x4_extract_lane(x[0], 3);        \
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/whisper-work/ggml/src/ggml-cpu/ggml-cpu.c:1640:9: warning: implicit conversion increases floating-point precision: 'float' to 'ggml_float' (aka 'double') [-Wdouble-promotion]
 1640 |         GGML_F16_VEC_REDUCE(sumf[k], sum[k]);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Users/danbev/work/ai/whisper-work/ggml/src/ggml-cpu/ggml-cpu.c:932:37: note: expanded from macro 'GGML_F16_VEC_REDUCE'
  932 | #define GGML_F16_VEC_REDUCE         GGML_F16x4_REDUCE
      |                                     ^
/Users/danbev/work/ai/whisper-work/ggml/src/ggml-cpu/ggml-cpu.c:920:44: note: expanded from macro 'GGML_F16x4_REDUCE'
  918 |     res = wasm_f32x4_extract_lane(x[0], 0) +       \
      |         ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  919 |           wasm_f32x4_extract_lane(x[0], 1) +       \
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  920 |           wasm_f32x4_extract_lane(x[0], 2) +       \
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~
  921 |           wasm_f32x4_extract_lane(x[0], 3);        \
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2 warnings generated.
```
wasm_f32x4_extract_lane returns a 32-bit float and this is what the
addition is performed on. But there is an implicit conversion from
32-bit float to 64-bit double when the result is assigned to `res`,
which is of type `ggml_float`. My understanding here is that this is
intentional and adding a cast to `ggml_float` should suppress the
warning.

Author: danbev

ggml/src/ggml-cpu/ggml-cpu.c

@@ -901,24 +901,24 @@ inline static void __wasm_f16x4_store(ggml_fp16_t * p, v128_t x) {
 #define GGML_F16x4_FMA         GGML_F32x4_FMA
 #define GGML_F16x4_ADD         wasm_f32x4_add
 #define GGML_F16x4_MUL         wasm_f32x4_mul
-#define GGML_F16x4_REDUCE(res, x)                  \
-{                                                  \
-    int offset = GGML_F16_ARR >> 1;                \
-    for (int i = 0; i < offset; ++i) {             \
-        x[i] = wasm_f32x4_add(x[i], x[offset+i]);  \
-    }                                              \
-    offset >>= 1;                                  \
-    for (int i = 0; i < offset; ++i) {             \
-        x[i] = wasm_f32x4_add(x[i], x[offset+i]);  \
-    }                                              \
-    offset >>= 1;                                  \
-    for (int i = 0; i < offset; ++i) {             \
-        x[i] = wasm_f32x4_add(x[i], x[offset+i]);  \
-    }                                              \
-    res = wasm_f32x4_extract_lane(x[0], 0) +       \
-          wasm_f32x4_extract_lane(x[0], 1) +       \
-          wasm_f32x4_extract_lane(x[0], 2) +       \
-          wasm_f32x4_extract_lane(x[0], 3);        \
+#define GGML_F16x4_REDUCE(res, x)                           \
+{                                                           \
+    int offset = GGML_F16_ARR >> 1;                         \
+    for (int i = 0; i < offset; ++i) {                      \
+        x[i] = wasm_f32x4_add(x[i], x[offset+i]);           \
+    }                                                       \
+    offset >>= 1;                                           \
+    for (int i = 0; i < offset; ++i) {                      \
+        x[i] = wasm_f32x4_add(x[i], x[offset+i]);           \
+    }                                                       \
+    offset >>= 1;                                           \
+    for (int i = 0; i < offset; ++i) {                      \
+        x[i] = wasm_f32x4_add(x[i], x[offset+i]);           \
+    }                                                       \
+    res = (ggml_float) (wasm_f32x4_extract_lane(x[0], 0) +  \
+          wasm_f32x4_extract_lane(x[0], 1) +                \
+          wasm_f32x4_extract_lane(x[0], 2) +                \
+          wasm_f32x4_extract_lane(x[0], 3));                \
 }
 
 #define GGML_F16_VEC                GGML_F16x4