[media] Fix undefined reference to `au8522_attach'

au8522_attach is dependent on CONFIG_DVB_AU8522_DTV, not CONFIG_DVB_AU8522.

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