Calculate inverse of output scale first. (#41342)
Summary:
This is to unify how output scale calculation is to be done between
fbgemm and qnnpack (servers vs mobile).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/41342
Test Plan: Quantization tests.
Reviewed By: vkuzo
Differential Revision: D22506347
Pulled By: kimishpatel
fbshipit-source-id: e14d22f13c6e751cafa3e52617e76ecd9d39dad5
