This fixes a subtle register allocation verifier bug: depending on how moves are 
optimized, and when having duplicate phis, we may end up overwriting a final
assessment.

Bug: 
Change-Id: I8b7891efbdd075aae0219d60270f405b13d50f40
Reviewed-on: https://chromium-review.googlesource.com/577288Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Mircea Trofin <mtrofin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46941}