[media] vivid: fix typo in plane size checks

The plane size check was hardcoded to plane 0 instead of using the plane
index.

This failed when using the NV61M format which has a larger plane size for
the second plane compared to the first plane.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>