fs: update location of filesystems documentation

The filesystem documentation was moved from DocBook to
Documentation/filesystems/. Update it at the sources.

Signed-off-by: Mauro Carvalho Chehab <[email protected]>
diff --git a/include/linux/debugfs.h b/include/linux/debugfs.h
index 9174b0d..aa86e6d 100644
--- a/include/linux/debugfs.h
+++ b/include/linux/debugfs.h
@@ -9,7 +9,7 @@
  *	2 as published by the Free Software Foundation.
  *
  *  debugfs is for people to use instead of /proc or /sys.
- *  See Documentation/DocBook/filesystems for more details.
+ *  See Documentation/filesystems/ for more details.
  */
 
 #ifndef _DEBUGFS_H_