[llvm] [CodeGen] computeRegisterProperties - fix `bf16` to `i16` bitcast quieting NaNs (PR #224867)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> Well both the class (float vs integer) and the size changed, so that that would cause churn kind of makes sense to me?

There are no float or integer registers, there are just registers. Also the size shouldn't change? 

https://github.com/llvm/llvm-project/pull/224867