[media] DocBook media: add missing dqevent src_change field

The v4l2_event union has a new src_change field, but that was never
added to the VIDIOC_DQEVENT documentation of that union. Fixed.
Signed-off-by: NHans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: NMauro Carvalho Chehab <m.chehab@samsung.com>

Documentation/DocBook/media/v4l/vidioc-dqevent.xml

@@ -98,6 +98,12 @@
             <entry><structfield>motion_det</structfield></entry>
 	    <entry>Event data for event V4L2_EVENT_MOTION_DET.</entry>
 	  </row>
+	  <row>
+	    <entry></entry>
+	    <entry>&v4l2-event-src-change;</entry>
+            <entry><structfield>src_change</structfield></entry>
+	    <entry>Event data for event V4L2_EVENT_SOURCE_CHANGE.</entry>
+	  </row>
 	  <row>
 	    <entry></entry>
 	    <entry>__u8</entry>