media: ov5647: Set V4L2_SUBDEV_FL_HAS_EVENTS flag

The ov5647 subdev can generate control events, therefore set
the V4L2_SUBDEV_FL_HAS_EVENTS flag.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>