net: lan966x: Fix potential null-ptr-deref in lan966x_stats_init()

lan966x_stats_init() calls create_singlethread_workqueue() and not
checked the ret value, which may return NULL. And a null-ptr-deref may
happen:

lan966x_stats_init()
    create_singlethread_workqueue() # failed, lan966x->stats_queue is NULL
    queue_delayed_work()
        queue_delayed_work_on()
            __queue_delayed_work()  # warning here, but continue
                __queue_work()      # access wq->flags, null-ptr-deref

Check the ret value and return -ENOMEM if it is NULL.

Fixes: 12c2d0a5 ("net: lan966x: add ethtool configuration and statistics")
Signed-off-by: Shang XiaoJing <shangxiaojing@huawei.com>
Reviewed-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/microchip/lan966x/lan966x_ethtool.c

@@ -716,6 +716,9 @@ int lan966x_stats_init(struct lan966x *lan966x)
 	snprintf(queue_name, sizeof(queue_name), "%s-stats",
 		 dev_name(lan966x->dev));
 	lan966x->stats_queue = create_singlethread_workqueue(queue_name);
+	if (!lan966x->stats_queue)
+		return -ENOMEM;
+
 	INIT_DELAYED_WORK(&lan966x->stats_work, lan966x_check_stats_work);
 	queue_delayed_work(lan966x->stats_queue, &lan966x->stats_work,
 			   LAN966X_STATS_CHECK_DELAY);