drm/omap: dispc: Simplify _dispc_mgr_set_lcd_timings() parameters

Instead of passing the omap_video_timings structure's members individually,
use the pointer to the struct.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>