[media] videobuf2-memops.h: add to device-drivers DocBook

The comment metadata was wrong:

Warning(.//include/media/videobuf2-memops.h:25): cannot understand function prototype: 'struct vb2_vmarea_handler '
Warning(.//include/media/videobuf2-memops.h): no structured comments found

Fix and add to DocBook.
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Acked-by: Jonathan Corbet <corbet@lwn.net>

Documentation/DocBook/device-drivers.tmpl

@@ -235,9 +235,9 @@ X!Isound/sound_firmware.c
 !Iinclude/media/v4l2-event.h
 !Iinclude/media/v4l2-dv-timings.h
 !Iinclude/media/videobuf2-core.h
+!Iinclude/media/videobuf2-memops.h
 <!-- FIXME: Removed for now due to document generation inconsistency
 X!Iinclude/media/v4l2-mediabus.h
-X!Iinclude/media/videobuf2-memops.h
 -->
 
   </chapter>

include/media/videobuf2-memops.h

@@ -17,7 +17,8 @@
 #include <media/videobuf2-core.h>
 
 /**
- * vb2_vmarea_handler - common vma refcount tracking handler
+ * struct vb2_vmarea_handler - common vma refcount tracking handler
+ *
  * @refcount:	pointer to refcount entry in the buffer
  * @put:	callback to function that decreases buffer refcount
  * @arg:	argument for @put callback