[InlineSpiller] Re-tie operands if folding failed

InlineSpiller::foldMemoryOperand unties registers before an attempt to fold and
does not restore tied-ness in case of failure.

I do not have a particular test for demo of invalid behavior.
This is something of clean-up.
It is better to keep the behavior correct in case some time in future it happens.

Reviewers: reames, dantrushin
Reviewed By: dantrushin, reames
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D94389