[quant][graphmode][fx][fix] Fix error that DefaultQuantizer is not inserted after a module configured with None qconfig (#47316)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/47316
Test Plan: Imported from OSS
Reviewed By: z-a-f
Differential Revision: D24713727
fbshipit-source-id: e604ef2274ff4bb4e8b6ebbb6ba681018e9ae248
