[Diagnostics] Call setMapping on the correct diagnostic states in a few...

[Diagnostics] Call setMapping on the correct diagnostic states in a few places. GetCurDiagState() was being used when it shouldn't be.

I spotted this by inspection in the for loop that wasn't using its iterator and was just acting on the current state repeatedly.

This appears to have been introduced as a copy and paste bug in r140763 over 4 years ago.

I have no idea how to test this. I just went back to the original commit and tried to use the variables it was using before that.

llvm-svn: 254134