V4L/DVB: V4L2 Spec: fix V4L2_CTRL_TYPE_CTRL_CLASS documentation

The spec says that the control ID for these types of controls is the same
as that of the control class. But it should read: 'control class + 1'.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

Documentation/DocBook/v4l/vidioc-queryctrl.xml

@@ -325,7 +325,7 @@ should be part of the control documentation.</entry>
 	    <entry>n/a</entry>
 	    <entry>This is not a control. When
 <constant>VIDIOC_QUERYCTRL</constant> is called with a control ID
-equal to a control class code (see <xref linkend="ctrl-class" />), the
+equal to a control class code (see <xref linkend="ctrl-class" />) + 1, the
 ioctl returns the name of the control class and this control type.
 Older drivers which do not support this feature return an
 &EINVAL;.</entry>