[SurfaceFlinger] correct present time for negative phase offsets

DispSync::expectedPresentTime returns the expected presentation time for
the current frame, but when we're in negative offsets we are targetting
the following frame instead.

Bug: 133241520
Bug: 134589085
Test: systrace when flinging through news
Change-Id: I7cc05a0b9e8e9b5c3e8d0c4b1d59b0a7dabd43d4
Merged-In: I7cc05a0b9e8e9b5c3e8d0c4b1d59b0a7dabd43d4