MAINTAINERS: Direct Documentation/DocBook/media properly

The media maintainers want DocBook changes to go through their tree;
document that wish accordingly.
diff --git a/MAINTAINERS b/MAINTAINERS
index b9b915663..11e2516 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -3440,6 +3440,7 @@
 X:	Documentation/acpi
 X:	Documentation/power
 X:	Documentation/spi
+X:	Documentation/DocBook/media
 T:	git git://git.lwn.net/linux-2.6.git docs-next
 
 DOUBLETALK DRIVER