media: v4l2-ctrls.c/uvc: zero v4l2_event

commit f45f3f753b0a3d739acda8e311b4f744d82dc52a upstream.

Control events can leak kernel memory since they do not fully zero the
event. The same code is present in both v4l2-ctrls.c and uvc_ctrl.c, so
fix both.

It appears that all other event code is properly zeroing the structure,
it's these two places.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reported-by:  <syzbot+4f021cf3697781dbd9fb@syzkaller.appspotmail.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>