switch open-coded instances of d_make_root() to new helper

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/ubifs/super.c b/fs/ubifs/super.c
index 63765d5..76e4e05 100644
--- a/fs/ubifs/super.c
+++ b/fs/ubifs/super.c
@@ -2076,15 +2076,13 @@
 		goto out_umount;
 	}
 
-	sb->s_root = d_alloc_root(root);
+	sb->s_root = d_make_root(root);
 	if (!sb->s_root)
-		goto out_iput;
+		goto out_umount;
 
 	mutex_unlock(&c->umount_mutex);
 	return 0;
 
-out_iput:
-	iput(root);
 out_umount:
 	ubifs_umount(c);
 out_unlock: