[media] DocBook media: fix fieldname in struct v4l2_subdev_selection

Field 'rect' is really named 'r'.
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

Documentation/DocBook/media/v4l/vidioc-subdev-g-selection.xml

@@ -119,7 +119,7 @@
 	  </row>
 	  <row>
 	    <entry>&v4l2-rect;</entry>
-	    <entry><structfield>rect</structfield></entry>
+	    <entry><structfield>r</structfield></entry>
 	    <entry>Selection rectangle, in pixels.</entry>
 	  </row>
 	  <row>