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/configfs/mount.c b/fs/configfs/mount.c
index 276e15c..07f6045 100644
--- a/fs/configfs/mount.c
+++ b/fs/configfs/mount.c
@@ -91,10 +91,9 @@
 		return -ENOMEM;
 	}
 
-	root = d_alloc_root(inode);
+	root = d_make_root(inode);
 	if (!root) {
 		pr_debug("%s: could not get root dentry!\n",__func__);
-		iput(inode);
 		return -ENOMEM;
 	}
 	config_group_init(&configfs_root_group);