Create a source pad and set the media controller type to the sensor.

Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: NJacopo Mondi <jacopo@jmondi.org>
Signed-off-by: NAkinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: NSakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab+samsung@kernel.org>