[llvm] [AMDGPU] Fix destination op_sel for v_cvt_scale32_* and v_cvt_sr_* (PR #151411)

[Changpeng Fang via llvm-commits]

changpeng wrote:

> Why not just `git revert` then?

Need to keep the part of src op_sel.  Only revert the dest part. 

https://github.com/llvm/llvm-project/pull/151411