[NNAPI] Rename local variable (#54698)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/54698
"mf" was short for memory format, but the concept that this variable
represents was renamed to "dim_order", so rename the variable.
Test Plan: Unit test
Reviewed By: axitkhurana
Differential Revision: D27536793
Pulled By: dreiss
fbshipit-source-id: 2b31c70da1ff221a7833e67486690fa606f01dea
