Mips: Don't create copy of nothing

This was creating a copy of the register the pseudo itself was
def'ing, leaving a copy of an undefined register. I'm not sure how
the verifier is not catching this, but this avoids asserting in a
future change to RegAllocFast

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@356716 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed