[llvm] [NVPTX] Use cvt.sat to lower min/max clamping to i8 and i16 ranges (PR #143016)

[Artem Belevich via llvm-commits]

https://github.com/Artem-B approved this pull request.

LGTM with a couple of nits.

https://github.com/llvm/llvm-project/pull/143016