fix quantization mechanism to match nnpi (#41494)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/41494
revert back to the changes from amylittleyang to make quantization work
Test Plan:
ran against a dump from ctr_instagram, and verified that:
-nnpi and fakelowp match bitwise
-nnpi is different at most by 1 vs fbgemm, most likely due to the type of
rounding
Reviewed By: venkatacrc
Differential Revision: D22555276
fbshipit-source-id: 7074521d181f15ef6270985bb71c4b44d25d1c30
