msm: mdss: fix crash when enabling autorefresh

Autorefresh feature does not need to issue a manual
flush in order to start processing the frames.
Remove the manual flush and make sure that we wait
for one vsync before suspend.

Change-Id: I557a1a67017d9f0171915c209479e22bd908db36
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>