[Cuda] Updated bfloat16 math defs.

Required to pass `test_cuda_bf16_vectorize_add` in `tests/python/unittest/test_target_codegen_cuda.py`.

Author: Lunderberg

src/target/source/literal/cuda_half_t.h

@@ -338,15 +338,15 @@ __pack_nv_bfloat162(const nv_bfloat16 x, const nv_bfloat16 y) {
 // so we define them here to make sure the generated CUDA code
 // is valid.
 #define CUDA_UNSUPPORTED_HALF_MATH_BINARY(HALF_MATH_NAME, FP32_MATH_NAME) \
-static inline __device__ __host__ half HALF_MATH_NAME(half x, half y) {   \
+static inline __device__ __host__ nv_bfloat16 HALF_MATH_NAME(nv_bfloat16 x, nv_bfloat16 y) {   \
   float tmp_x = __bfloat162float(x);                                      \
   float tmp_y = __bfloat162float(y);                                      \
   float result = FP32_MATH_NAME(tmp_x, tmp_y);                            \
   return __float2bfloat16(result);                                        \
 }
 
 #define CUDA_UNSUPPORTED_HALF_MATH_UNARY(HALF_MATH_NAME, FP32_MATH_NAME) \
-static inline __device__ __host__ half HALF_MATH_NAME(half x) {          \
+static inline __device__ __host__ nv_bfloat16 HALF_MATH_NAME(nv_bfloat16 x) {          \
   float tmp_x = __bfloat162float(x);                                     \
   float result = FP32_MATH_NAME(tmp_x);                                  \
   return __float2bfloat16(result);                                       \