Fix quantization doc issue (#50187)
Summary:
There has a description error in quantization.rst, fixed it.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/50187
Reviewed By: mrshenli
Differential Revision: D25895294
Pulled By: soumith
fbshipit-source-id: c0b2e7ba3fadfc0977ab2d4d4e9ed4f93694cedd
