ovl: update MAINTAINERS

There's a union/overlay specific mailing list now.  Also add a git tree.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

MAINTAINERS

@@ -6890,9 +6890,10 @@ F:	fs/exofs/
 
 OVERLAY FILESYSTEM
 M:	Miklos Szeredi <miklos@szeredi.hu>
-L:	linux-fsdevel@vger.kernel.org
+L:	linux-unionfs@vger.kernel.org
+T:	git git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs.git
 S:	Supported
-F:	fs/overlayfs/*
+F:	fs/overlayfs/
 F:	Documentation/filesystems/overlayfs.txt
 
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