[quant][qat] Ensure observers and fq modules are scriptable (#44749)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/44749
Ensure fx module is scriptable after calling prepare_qat on it
Test Plan:
python test/test_quantization.py TestQuantizeFx.test_qat_and_script
Imported from OSS
Reviewed By: jerryzh168
Differential Revision: D23718380
fbshipit-source-id: abf63ffb21e707f7def8f6c88246877f5aded58c
