msm: mdss: wait for one commit transfer for command mode after resume

In command mode, the backlight level is set before the first commit
is completed. It shows a snowy screen after suspend resume. Wait for
one ping pong done to ensure commit is completed after suspend
resume before backlight level is set.

Change-Id: I2c6da73f3f84bcdf84e5b90c64f9ca05f0c27198
Signed-off-by: Ashish Garg <ashigarg@codeaurora.org>