TableGen: Only fold when some operand made resolve progress

Summary:
Make sure that we always fold immediately, so there's no point in
attempting to re-fold when nothing changes.

Change-Id: I069e1989455b6f2ca8606152f6adc1a5e817f1c8

Reviewers: arsenm, craig.topper, tra, MartinO

Subscribers: wdng, llvm-commits

Differential Revision: https://reviews.llvm.org/D44198

llvm-svn: 327847