media: media/common/saa7146: rename VFL_TYPE_GRABBER to _VIDEO

'GRABBER' is a weird name, all other types map to the /dev
device names. Rename to 'VIDEO' to be consistent with the
other types.

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