msm: display: reset vsync state when display is turned on

In the case that vsync ctrl is unbalanced, vsync IRQ is cleared
in suspend,  vsync cannot be enabled after resume.
Clear the status when display is turned on

CRs-fixed: 449155
Change-Id: I5ecf23053b60d1fbd91f042758d67d39c83ab444
Signed-off-by: Ken Zhang <kenz@codeaurora.org>

Conflicts:

	drivers/video/msm/mdp4_overlay_dsi_video.c