Format reducer.cpp, hpp (#58593)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/58593
Per title
ghstack-source-id: 129498230
Test Plan: CI
Reviewed By: zhaojuanmao
Differential Revision: D28528465
fbshipit-source-id: 89e4bfcb4a0275dc17090a934d4c0a41a3c54046
