[MLIR][EmitC] arith-to-emitc: Fix lowering of fptoui (#118504)

`arith.fptoui %arg0 : f32 to i16` was lowered to
```
%0 = emitc.cast %arg0 : f32 to ui32
emitc.cast %0 : ui32 to i16
```
and is now lowered to
```
%0 = emitc.cast %arg0 : f32 to ui16
emitc.cast %0 : ui16 to i16
```

Author: mgehre-amd

mlir/lib/Conversion/ArithToEmitC/ArithToEmitC.cpp

@@ -674,7 +674,7 @@ class FtoICastOpConversion : public OpConversionPattern<CastOp> {
     Type actualResultType = dstType;
     if (isa<arith::FPToUIOp>(castOp)) {
       actualResultType =
-          rewriter.getIntegerType(operandType.getIntOrFloatBitWidth(),
+          rewriter.getIntegerType(dstType.getIntOrFloatBitWidth(),
                                   /*isSigned=*/false);
     }
 

mlir/test/Conversion/ArithToEmitC/arith-to-emitc.mlir

@@ -587,6 +587,10 @@ func.func @arith_float_to_int_cast_ops(%arg0: f32, %arg1: f64) {
   // CHECK: emitc.cast %[[CAST0]] : ui32 to i32
   %4 = arith.fptoui %arg0 : f32 to i32
 
+  // CHECK: %[[CAST0:.*]] = emitc.cast %arg0 : f32 to ui16
+  // CHECK: emitc.cast %[[CAST0]] : ui16 to i16
+  %5 = arith.fptoui %arg0 : f32 to i16
+
   return
 }