[media] adp1653: set media entity type

The type of a media entity is default for this driver. This patch makes it
explicitly defined as MEDIA_ENT_T_V4L2_SUBDEV_FLASH.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>