virtio: console: fix error handling in init() function

If register_virtio_driver() fails, virtio-ports class is not destroyed.
The patch adds error handling of register_virtio_driver().

Found by Linux Driver Verification project (linuxtesting.org).
Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Acked-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

drivers/char/virtio_console.c

@@ -2099,7 +2099,17 @@ static int __init init(void)
 	INIT_LIST_HEAD(&pdrvdata.consoles);
 	INIT_LIST_HEAD(&pdrvdata.portdevs);
 
-	return register_virtio_driver(&virtio_console);
+	err = register_virtio_driver(&virtio_console);
+	if (err < 0) {
+		pr_err("Error %d registering virtio driver\n", err);
+		goto free;
+	}
+	return 0;
+free:
+	if (pdrvdata.debugfs_dir)
+		debugfs_remove_recursive(pdrvdata.debugfs_dir);
+	class_destroy(pdrvdata.class);
+	return err;
 }
 
 static void __exit fini(void)