V4L: ivtv/cx18: fix regression: class controls are no longer seen

V4L: ivtv/cx18: fix regression: class controls are no longer seen

(cherry picked from commit c6711c3e6d4976716633047c0f6bbd953d6831fb)

A previous change (v4l2-common: remove v4l2_ctrl_query_fill_std) broke
the handling of class controls in VIDIOC_QUERYCTRL. The MPEG class control
was broken for all drivers that use the cx2341x module and the USER class
control was broken for ivtv and cx18.

This change adds back proper class control support.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>