media: i2c: ov5647: Tidy up PIXEL_RATE control

media: i2c: ov5647: Tidy up PIXEL_RATE control

The pixel rate control is marked as read-only by the framework itself,
so no need to mark it explicitly in the driver. Also, we can set the ops
to NULL to avoid checking for it in the s_ctrl implementation.

Suggested-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Signed-off-by: Jai Luthra <jai.luthra@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>