firmware: fix detecting error on register_reboot_notifier()

register_reboot_notifier() can fail, detect this and address this
failure. This has been broken since v3.11, however the chances of
this failing here is really low.

Fixes: fe304143 ("firmware: Avoid deadlock of usermodehelper lock at shutdown")
Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/base/firmware_class.c

@@ -1860,8 +1860,15 @@ static int __init firmware_class_init(void)
 	if (ret)
 		return ret;
 
-	register_reboot_notifier(&fw_shutdown_nb);
+	ret = register_reboot_notifier(&fw_shutdown_nb);
+	if (ret)
+		goto out;
+
 	return register_sysfs_loader();
+
+out:
+	unregister_fw_pm_ops();
+	return ret;
 }
 
 static void __exit firmware_class_exit(void)