Update DBG_VALUE register operand during LiveInterval operations

Summary:
Handling of DBG_VALUE in ConnectedVNInfoEqClasses::Distribute() was fixed in
PR16110. However DBG_VALUE register operands are not getting updated. This
patch properly resolves the value location.

Reviewers: MatzeB, vsk

Reviewed By: MatzeB

Subscribers: kparzysz, thegameg, vsk, MatzeB, dschuff, sbc100, jgravelle-google, aheejin, sunfish, llvm-commits

Tags: #debug-info

Differential Revision: https://reviews.llvm.org/D48994

llvm-svn: 340310