[media] v4l2-dv-timings.h: let kernel-doc parte the typedef argument

Now that scripts/kernel-doc was fixed to parse the typedef
argument used here, let it produce documentation.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

include/media/v4l2-dv-timings.h

@@ -28,8 +28,8 @@
  */
 extern const struct v4l2_dv_timings v4l2_dv_timings_presets[];
 
-/*
- * v4l2_check_dv_timings_fnc - timings check callback
+/**
+ * typedef v4l2_check_dv_timings_fnc - timings check callback
  *
  * @t: the v4l2_dv_timings struct.
  * @handle: a handle from the driver.