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/fuse/inode.c b/fs/fuse/inode.c
index 64cf8d0..4aec599 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -988,14 +988,9 @@
 
 	err = -ENOMEM;
 	root = fuse_get_root_inode(sb, d.rootmode);
-	if (!root)
+	root_dentry = d_make_root(root);
+	if (!root_dentry)
 		goto err_put_conn;
-
-	root_dentry = d_alloc_root(root);
-	if (!root_dentry) {
-		iput(root);
-		goto err_put_conn;
-	}
 	/* only now - we want root dentry with NULL ->d_op */
 	sb->s_d_op = &fuse_dentry_operations;