Fix broadcasting of cdist backward (#56605)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/56605
Fix https://github.com/pytorch/pytorch/issues/55370
Test Plan: Imported from OSS
Reviewed By: ailzhang
Differential Revision: D27939202
Pulled By: albanD
fbshipit-source-id: a4ac50a7b504c24f47f5343414fb57523546a0c7
