On format change, sometimes, sensor was streaming at a much higher
FPS than the default. This was resulting in various problems like
frame drops/corruption.

Upon format change, set default vblank as current vblank. This will
ensure that sensor will start streaming at default fps.
Signed-off-by: NChiranjeevi Rapolu <chiranjeevi.rapolu@intel.com>
Signed-off-by: NSakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@s-opensource.com>