V4L/DVB: tm6000: Partially revert some copybuf logic

Partially revert changeset 0208bef609242a2d50b95edc713a41566cae500b:

As pointed by Stefan Ringel <stefan.ringel@arcor.de>, many packets become
damaged by this change. That means that the "size" field of Video/VBI is not
presenting 180 bytes, as it should be expected.

Thanks-to: Stefan Ringel <stefan.ringel@arcor.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>