V4L/DVB (9265): videobuf: data storage optimisation

To optimise data storage redundant vars are removed.

Signed-off-by: Darron Broad <darron@kewl.org>
Signed-off-by: Steven Toth <stoth@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>