[clang] [clang] fix half && bfloat16 convert node expr codegen (PR #89051)

[Craig Topper via cfe-commits]

topperc wrote:

> > @JinjinLi868 are you still working on this?
> 
> I can ask him. Is this PR blocking some of your recent works on float16/bf16?

I stumbled onto the verifier error earlier while writing a test. It's not blocking me.

https://github.com/llvm/llvm-project/pull/89051