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/romfs/super.c b/fs/romfs/super.c
index bb36ab7..e64f6b5 100644
--- a/fs/romfs/super.c
+++ b/fs/romfs/super.c
@@ -538,14 +538,12 @@
 	if (IS_ERR(root))
 		goto error;
 
-	sb->s_root = d_alloc_root(root);
+	sb->s_root = d_make_root(root);
 	if (!sb->s_root)
-		goto error_i;
+		goto error;
 
 	return 0;
 
-error_i:
-	iput(root);
 error:
 	return -EINVAL;
 error_rsb_inval: