[Gradient Compression] Update the docstring of fp16_compress_hook (#58168)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/58168
Update the documentation to be consistent to https://github.com/pytorch/pytorch/pull/57410.
ghstack-source-id: 128797174
Test Plan: N/A
Reviewed By: agolynski, zhengwy888
Differential Revision: D28388160
fbshipit-source-id: 6ba13ad9f9d7b4d003cdc112545573e452df8b65
