V4L/DVB (9271): videobuf: data storage optimisation (2)

To optimise data storage even further one other redundant
var has been removed.

This also removes a redundant assignment.

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