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

[Folkert de Vries via llvm-commits]

folkertdev wrote:

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

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