[media] v4l2-ioctl: make tuner 'type' check more strict for S_FREQUENCY

As per the feature removal document, make the tuner type check more strict
so that it is no longer possible to set the radio frequency through a video
node or the TV frequency through a radio node.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

Documentation/DocBook/media/v4l/vidioc-g-frequency.xml

@@ -98,8 +98,11 @@ the &v4l2-output; <structfield>modulator</structfield> field and the
 	    <entry>&v4l2-tuner-type;</entry>
 	    <entry><structfield>type</structfield></entry>
 	    <entry>The tuner type. This is the same value as in the
-&v4l2-tuner; <structfield>type</structfield> field. The field is not
-applicable to modulators, &ie; ignored by drivers.</entry>
+&v4l2-tuner; <structfield>type</structfield> field. The type must be set
+to <constant>V4L2_TUNER_RADIO</constant> for <filename>/dev/radioX</filename>
+device nodes, and to <constant>V4L2_TUNER_ANALOG_TV</constant>
+for all others. The field is not applicable to modulators, &ie; ignored
+by drivers.</entry>
 	  </row>
 	  <row>
 	    <entry>__u32</entry>