UBIFS: switch to I/O helpers

Switch the rest of direct UBI calls to UBIFS helper functions.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
diff --git a/fs/ubifs/super.c b/fs/ubifs/super.c
index 2850385..b281212 100644
--- a/fs/ubifs/super.c
+++ b/fs/ubifs/super.c
@@ -914,7 +914,7 @@
 
 	c->empty = 1;
 	for (lnum = 0; lnum < c->leb_cnt; lnum++) {
-		err = ubi_is_mapped(c->ubi, lnum);
+		err = ubifs_is_mapped(c, lnum);
 		if (unlikely(err < 0))
 			return err;
 		if (err == 1) {