msm: mdss: flush timing after splash done for video panel

During continuous splash handoff the pipes are unstaged and the
timing engine is being turned off. But this change is not
being flushed. Right after that we release the splash memory
and this sometimes causes a memory fault. This change adds
the necessary flush.

Change-Id: Ia78359fd8159a7217ffc4f0192788f295ac3504c
Signed-off-by: Rajkumar Subbiah <rsubbia@codeaurora.org>