[media] vidioc-enumstd.rst: fix a broken reference

Somehow, the conversion broke a reference here. Re-add it.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
diff --git a/Documentation/media/uapi/v4l/vidioc-enumstd.rst b/Documentation/media/uapi/v4l/vidioc-enumstd.rst
index 6699b26..a936fe3 100644
--- a/Documentation/media/uapi/v4l/vidioc-enumstd.rst
+++ b/Documentation/media/uapi/v4l/vidioc-enumstd.rst
@@ -269,7 +269,7 @@
 
 .. _video-standards:
 
-.. flat-table:: Video Standards (based on [])
+.. flat-table:: Video Standards (based on :ref:`itu470`)
     :header-rows:  1
     :stub-columns: 0