add fp16 kernel to clip_grad (#41675)

paddle/phi/kernels/gpu/clip_grad_kernel.cu

@@ -15,6 +15,7 @@
 #include "paddle/phi/kernels/clip_grad_kernel.h"
 
 #include "paddle/phi/backends/gpu/gpu_context.h"
+#include "paddle/phi/common/float16.h"
 #include "paddle/phi/core/kernel_registry.h"
 #include "paddle/phi/kernels/impl/clip_grad_kernel_impl.h"
 
@@ -25,4 +26,5 @@ PD_REGISTER_KERNEL(clip_grad,
                    float,
                    double,
                    int,
-                   int64_t) {}
+                   int64_t,
+                   phi::dtype::float16) {}