[media] m2m-deinterlace: use correct check for kzalloc failure

There is no point in PTR_ERR()ing a NULL pointer, use a real error
instead.

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>