[MemorySSA] Pass DT to the upward iterator for proper PhiTranslation.

Summary:
A valid DominatorTree is needed to do PhiTranslation.
Before this patch, a MemoryUse could be optimized to an access outside a loop, while the address it loads from is modified in the loop.
This can lead to a miscompile.

Reviewers: george.burgess.iv

Subscribers: Prazek, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D79068