[OpenCL] Fix inconsistency between opencl and c11 atomic fetch max/min

There is some inconsistency between opencl and c11 atomic fetch max/min after

https://reviews.llvm.org/D46386

https://reviews.llvm.org/D55562

It is not reasonable to have such inconsistencies. This patch fixes that.

Differential Revision: https://reviews.llvm.org/D71725