Fix clip_by_norm_op error message. test=develop

paddle/fluid/operators/clip_by_norm_op.h

@@ -63,8 +63,8 @@ class ClipByNormKernel : public framework::OpKernel<T> {
       output->Resize(merged_input->value().dims());
       output->mutable_data<T>(context.GetPlace());
     } else {
-      PADDLE_THROW("Unexpected branch, input variable type is %s",
-                   framework::ToTypeName(in_var->Type()));
+      PADDLE_THROW(
+          platform::errors::InvalidArgument("invalid input variable type"));
     }
 
     PADDLE_ENFORCE_NOT_NULL(input,