vulkan: fix shmem overrun in mmq id shader

Author: 0cc4m

ggml/src/ggml-vulkan/vulkan-shaders/mul_mmq.comp

@@ -83,8 +83,12 @@ layout (constant_id = 10) const uint WARP = 32;
 #include "mul_mmq_shmem_types.glsl"
 
 #ifndef BK_STEP
+#ifdef MUL_MAT_ID
+#define BK_STEP 1
+#else
 #define BK_STEP 4
 #endif
+#endif
 
 // Shared memory cache
 shared block_a_cache buf_a[BM * BK_STEP];