Add size check for forward grads (#54100)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/54100
Test Plan: Imported from OSS
Reviewed By: ejguan
Differential Revision: D27117842
Pulled By: albanD
fbshipit-source-id: ccb6abac38d7fca31bea72cbbf3bba38c6030c37
