fix missing std (#17263)
Summary:
add missing std introduced by #16689 . Investigating why this wasn't caught in CI (nor my local dev environment).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/17263
Reviewed By: ezyang
Differential Revision: D14134556
Pulled By: ailzhang
fbshipit-source-id: 6f0753fa858d3997e654924779646228d6d49838
