media: vivid: fix vid_out_buf_prepare()

The wrong size check was performed for output formats like NV24 which
set vfmt->buffers to 1, but vfmt->planes is 2. It was incorrectly
checking the payload size for plane 1, which doesn't exist.

Note: vfmt->buffers refers to the number of per-plane-buffers that
should be allocated. vfmt->planes refers to the number of planes
that make up an image. vfmt->planes may be > vfmt->buffers.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>