[SubZero] Fix code generation of AtomicCmpxchg

The patch fixes a code generation issue occurred in the 2nd iteration of LL-SC loop.

R=stichnot@chromium.org

Patch from Jaydeep Patil <jaydeep.patil@imgtec.com>.

Review-Url: https://codereview.chromium.org/2656723003 .
2 files changed