[fx_const_fold] Fix constant folding for attrs in submodule hierarchies (#64342)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/64342
Previously we weren't handling the case where an attribute was in a module that wasn't the root.
Test Plan: Added unit test coverage.
Reviewed By: yinghai
Differential Revision: D30691730
fbshipit-source-id: b39b5cf748c4c882f315a4f32b51ad88cc7a43ed
