[media] v4l: Fix a use-before-set in the control framework

v4l2_queryctrl sets the step value based on the control type. That would
be fine if it used the control type stored in the V4L2 kernel control
object, not the one stored in the userspace ioctl structure that has
just been memset to 0. Fix this.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>