msmfb: display: fix the issue with overlay wait api

calling overlay wait api asynchronous to the other overlay apis
results in race condition in protection flags. this case is
observed with HDMI true mirroring feature. it modifies the
protection logic to fix the race condition

Change-Id: Ib933055a395c2fc743f018aee96090defde33d37
Signed-off-by: Nagamalleswararao Ganji <nganji@codeaurora.org>