media-devnode: just return 0 instead of using a var

commit 8b37c645

 upstream.

Instead of allocating a var to store 0 and just return it,
change the code to return 0 directly.

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>