Int8 FC fix to match NNPI ICE-REF step-C (#48459)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/48459
Bias should be kept it in FP32. There is no need to convert the bias to FP16.
Test Plan: https://internalfb.com/intern/testinfra/testrun/562950128141661
Reviewed By: hyuen
Differential Revision: D25179863
fbshipit-source-id: e25d948c613d2b2d5adf2b674fc2ea4b4c8d3920
