Fix batch norm multiplier init (#13774)
Summary:
Fixes #12259, needs to make sure tests (see #13766) don't break due to numerical precision issues. Not sure what would need to be adjusted here...
Pull Request resolved: https://github.com/pytorch/pytorch/pull/13774
Differential Revision: D15715021
Pulled By: ezyang
fbshipit-source-id: 20ce2beee1b39ebe9f023c5f2b25be53acccb5f3
