[quant][eagermode][fix] Fix quantization for DeQuantStub (#49428)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/49428
Previously dequantstub will be swapped with nn.quantized.DeQuantize regardless of qconfig
reason is we skipped attaching qconfig for DeQuantStub to avoid adding fake quantize module to it
but the correct fix is to skip it in insert observers, this PR fixes the issue.
Test Plan: Imported from OSS
Reviewed By: vkuzo
Differential Revision: D25569991
fbshipit-source-id: d44a08c6e64c7a49509687dc389b57de1cbb878c
