add reg for fp16 pad to save time for ml_object_detect

mindspore/lite/src/runtime/kernel/arm/fp16/pad_fp16.cc

@@ -110,4 +110,5 @@ kernel::LiteKernel *CpuPadFp16KernelCreator(const std::vector<lite::Tensor *> &i
   }
   return kernel;
 }
+REG_KERNEL(kCPU, kNumberTypeFloat16, PrimitiveType_Pad, CpuPadFp16KernelCreator)
 }  // namespace mindspore::kernel