Recommit "[RISCV] Use setcc's original SDLoc when inverting it in performSUBCombine."

This time using N1 instead of N0 since N1 points to the original
setcc. This now affects scheduling as I expected.

Original commit message:
We change seteq<->setne but it doesn't change the semantics
of the setcc. We should keep original debug location. This is
consistent with visitXor in the generic DAGCombiner.