[media] rc: unlock on error in store_protocols()

This error path is missing the unlock.

[mchehab@redhat.com: Merged two equal patches into one]
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Acked-by: David Härdeman <david@hardeman.nu>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>