media: v4l2-compat-ioctl32.c: zero buffer passed to v4l2_compat_get_array_args()

The v4l2_compat_get_array_args() function can leave uninitialized memory in the
buffer it is passed. So zero it before copying array elements from userspace
into the buffer.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reported-by:  <syzbot+ff18193ff05f3f87f226@syzkaller.appspotmail.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>