[FX] Fix mypy error in FX for rewriter (#51740)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/51740
Reviewed By: jamesr66a
Differential Revision: D26261009
Pulled By: Chillee
fbshipit-source-id: ce97316aede5509fc8ed90b4eb6b758e2bc1fa7a
