[media] smiapp: Return correct return value in smiapp_registered()

Prepare for supporting systems using the Device tree. Should the resources
not be available at the time of driver probe(), the EPROBE_DEFER error code
must be also returned from its probe function.

Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>