[llvm] [NVPTX][NFC] Update tests to use bfloat type (PR #101493)

[Justin Fargnoli via llvm-commits]

justinfargnoli wrote:

@hdelan, if you're interested, here's the documentation on [obtaining commit access](https://llvm.org/docs/DeveloperPolicy.html#obtaining-commit-access),

https://github.com/llvm/llvm-project/pull/101493