[media] v4l: vsp1: Rename vsp1_video_buffer to vsp1_vb2_buffer

The structure represent a vsp1 videobuf2 buffer, name it accordingly.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>