media: staging/media/omap4iss/iss_video.c: videobuf -> vb2

Rename 'videobuf' to 'vb2' in the comment. This avoids confusing
terminology since 'videobuf' typically refers to the old vb1
framework.

Signed-off-by: Hans Verkuil <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/staging/media/omap4iss/iss_video.c

···
  * processing might be possible but requires more testing.
  *
  * Stream start must be delayed until buffers are available at both the input
- * and output. The pipeline must be started in the videobuf queue callback with
+ * and output. The pipeline must be started in the vb2 queue callback with
  * the buffers queue spinlock held. The modules subdev set stream operation must
  * not sleep.
  */