[NVPTX] Fix lit test issues from masked load/store implementation (#169535)
From this commit:
https://github.com/llvm/llvm-project/commit/17852deda7fb9dabb41023e2673025c630b9369d,
Build was broken here:
https://lab.llvm.org/buildbot/#/builders/155/builds/15135/steps/7/logs/stdio.
I think this should fix things.