Don't run comparisons on non-jank frames

Unclear why mSwapDeadline doesn't already
account for this, but the handling of vsync
phase offsets may be throwing things off a bit.

For now just do the simple fix.

Bug: 109894489
Test: builds, patch was verified by reporter
Change-Id: I5a6f25ceac4986d366293fe7b5e3af64a326114c