[media] stk1160: unlock on error path stk1160_set_alternate()

There are some unlocks missing on error.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Ezequiel Garcia <elezegarcia@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>