[media] smiapp: Set sub-device owner

The smiapp driver is the owner of the sub-devices exposed by the smiapp
driver. This prevents unloading the module whilst it's in use.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>