[te] Fix pow (#48213)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/48213
it was completely broken unless rhs was a constant.
Test Plan: new unit test in test_jit_fuser_te.py
Reviewed By: eellison
Differential Revision: D25071639
fbshipit-source-id: ef1010a9fd551db646b83adfaa961648a5c388ae
