media: gspca: convert to vb2

The gspca core has its own buffere implementation. Use the
core VB 2 instead.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>