[fbgemm] fix bug handling bias in rowwise quantization of FC (#58022)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/58022
Caffe2 Int8FC + rowwise quantization was not handling bias correctly.
Test Plan: The example in D28347336 doesn't show bigger error with rowwise quantization any more
Reviewed By: hx89, janeyx99
Differential Revision: D28347336
fbshipit-source-id: 3ac95fd2f29ef6e52705c3a2361b605813c2bcc5
