commit a9ae4692 upstream.

It's also invalid when plane_no is equal to vb->num_planes
Signed-off-by: Zhaowei Yuan <zhaowei.yuan@samsung.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
[bwh: Backported to 3.2: adjust filename, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>