RenameIndependentSubregs: Fix infinite loop

Apparently this replacement can really be substituting the
same as the original register. Avoid restarting the loop
when there's been no change in the register uses.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@306441 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed