TargetInstrInfo::commuteInstruction() doesn't actually return a new instruction
unless it was requested to with an optional parameter that defaults to false, so
we don't need to handle that case in TwoAddressInstructionPass.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175974 91177308-0d34-0410-b5e6-96231b3b80d8