[BE] Pass masked_fill_inplace_if_safe tensor argument by const reference (#194646)

Fixes pre-existing clang-tidy `performance-unnecessary-value-param` error, which fails lint for any PR touching `FunctionsManual.cpp`. Discovered while working on grouped_mm for MPS.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/194646
Approved by: https://github.com/Skylion007