[media] Add missing slab.h to fix linux-next compile errors

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reported-by: Randy Dunlap <rdunlap@xenotime.net>
Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
8 files changed