Programming the sensor with TIMING_VTS (aka LPFR) was done
when triggered by a change in exposure or gain, but not
when V4L2_CID_VBLANK was changed. Dynamic frame rate
changes could therefore not be achieved.

Separate out programming TIMING_VTS so that it is triggered
by set_ctrl(V4L2_CID_VBLANK)
Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>