media: v4l2-ioctl: Clear only per-plane reserved fields

Currently the IOCTL code clears everything after the per-plane
bytesperline field in struct v4l2_format. The intent was to only clear
the per-plane reserved fields since there is data in struct v4l2_format
after the per-plane format data that userspace may have filled in.

Fixes: 4e1e0eb0 ("media: v4l2-ioctl: Zero v4l2_plane_pix_format reserved fields")

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
[hverkuil-cisco@xs4all.nl: fix checkpatch alignment warning]
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>