SurfaceFlinger: DispSync: negative offsets when model is unlocked

When getting a HWVsync timestamp in DispSync, we correct the last event
time to reflect the actual HWVsync time by setting it based on HWVsync.
This logic needs to account for both positive and negative offsets.

Bug: 135631964
Test: sanity
Change-Id: I77a1e13d739e558d6cdf43c298e6fcee49d517b5
(cherry picked from commit 81ca00ff8cd05913fe0e97e0f97b3a9ae7ed3299)
1 file changed