Ensure we are diffing against the right thing in clang-format (#37589)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/37589
Apply the fix from https://github.com/pytorch/pytorch/commit/9f890a92 to
the clang-format job as well.
Test Plan: Imported from OSS
Differential Revision: D21330250
Pulled By: suo
fbshipit-source-id: d92b9666ba8b92d049393cbe7f2ce45daa563910
