MAINTAINERS: update cifs location

Commit 30706a54 ("cifs: create a new Documentation/ directory and
move docfiles into it") moved the files, update the pattern.
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

MAINTAINERS

@@ -2415,7 +2415,7 @@ W:	http://linux-cifs.samba.org/
 Q:	http://patchwork.ozlabs.org/project/linux-cifs-client/list/
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/sfrench/cifs-2.6.git
 S:	Supported
-F:	Documentation/filesystems/cifs.txt
+F:	Documentation/filesystems/cifs/
 F:	fs/cifs/
 
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