media: i2c: Add .get_selection() support to ov8865

The ov8865 driver's v4l2_subdev_pad_ops currently does not include
.get_selection() - add support for that callback.

Signed-off-by: Daniel Scally <djrscally@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>