hwc: Reset mode tracking in MDPComp constructor

Short story: This missing initialization fixes a crash in SF during
bootup on video mode panels with idle timeout.

Long story: SF creates HWC which registers a timeout handler. The
driver triggers this without even a composition round happening.
The junk value in mode tracking in MDPComp allows this timeout to
get translated into an invalidate() on SF. At this point SF may
not have fully created its EventThread (timing issue), which causes
a crash during bootup.

Change-Id: Icc91391399b2c0a027957be0689a226b5b1da783
1 file changed