UBIFS: add debugfs support

We need to have a possibility to see various UBIFS variables
and ask UBIFS to dump various information. Debugfs is what
we need.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
diff --git a/fs/ubifs/ubifs.h b/fs/ubifs/ubifs.h
index 7e090a5..4cf28e8 100644
--- a/fs/ubifs/ubifs.h
+++ b/fs/ubifs/ubifs.h
@@ -1158,6 +1158,7 @@
  * @mount_opts: UBIFS-specific mount options
  *
  * @dbg: debugging-related information
+ * @dfs: debugfs support-related information
  */
 struct ubifs_info {
 	struct super_block *vfs_sb;