[quant][graphmode][fx][api] Call fuse in prepare (#43984)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/43984
Test Plan: Imported from OSS
Reviewed By: vkuzo
Differential Revision: D23459261
fbshipit-source-id: 6b56b0916d76df67b9cc2f4be1fcee905d604019
