[media] smiapp: Free control handlers in sub-device cleanup

Also call smiapp_cleanup() in smiapp_remove(), replacing code that did the
same than the function.

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