media: avoid use of 'videobuf'

The term 'videobuf' typically refers to the old videobuf version 1
framework. Avoid using this word in drivers that are converted to
vb2.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>