[media] saa7164: remove unused videobuf references

This driver includes videobuf headers and selects VIDEOBUF_DVB, but
videobuf isn't used at all.

Remove this.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>