drm/msm/sde: increase wait time for ctl_start irq

It may possible that sde driver triggers the frame
on read_ptr boundary. That may miss the current vsync
cycle kickoff window and frame is picked up on next
vsync_cycle. This may cause to generate the ctl_start
at 2 vsync boundary and fail the ctl_start wait. A 4
vsync wait increase allows remove such false alarm
from ctl_start error

Change-Id: I1051c4dc443f338a3cf158815d3db9cc52d6db3c
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>