typo in docs ddp_comm_hooks.rst (#51986)
Summary:
Fixes a typo in ddp_comm_hooks.rst
Pull Request resolved: https://github.com/pytorch/pytorch/pull/51986
Reviewed By: SciPioneer
Differential Revision: D26360314
Pulled By: mrshenli
fbshipit-source-id: 50349501c53823cbcbad0f72be7c6ac9d51a4120
