MAINTAINERS: Add file pattern for fb dt bindings.

Now that Documentation/devicetree/bindings/fb/ exists, make sure it's
also matched by the default framebuffer entry.
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

MAINTAINERS

@@ -2633,6 +2633,7 @@ Q:	http://patchwork.kernel.org/project/linux-fbdev/list/
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/lethal/fbdev-2.6.git
 S:	Orphan
 F:	Documentation/fb/
+F:	Documentation/devicetree/bindings/fb/
 F:	drivers/video/
 F:	include/video/
 F:	include/linux/fb.h