R600/SI: Remove redundant legalizeOperands call

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194749 91177308-0d34-0410-b5e6-96231b3b80d8
When folding memory operands, preserve existing MachineMemOperands.

This comes into play with patchpoint, which can fold multiple
operands. Since the patchpoint is already treated as a call, the
machine mem operands won't affect anything, and there's nothing to
test. But we still want to do the right thing here to be sure that our
MIs obey the rules.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194750 91177308-0d34-0410-b5e6-96231b3b80d8