[media] smiapp: Use devm_* functions in smiapp-core.c file

devm_* functions are device managed functions and make code a bit
smaller and cleaner.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>