[AMDGPU] Fix OpenCL conformance test failures for ctlz. (#83170)

Remove LSH transform and restore previous lowering.

Fixes conformance issue in
[77615](https://github.com/llvm/llvm-project/pull/77615

) where OpenCL
integer_ops tests fail for integer_clz.

Co-authored-by: Leon Clark <leoclark@amd.com>