wifi: carl9170: do not ping device which has failed to load firmware

Syzkaller reports [1, 2] crashes caused by an attempts to ping
the device which has failed to load firmware. Since such a device
doesn't pass 'ieee80211_register_hw()', an internal workqueue
managed by 'ieee80211_queue_work()' is not yet created and an
attempt to queue work on it causes null-ptr-deref.

[1] https://syzkaller.appspot.com/bug?extid=9a4aec827829942045ff
[2] https://syzkaller.appspot.com/bug?extid=0d8afba53e8fb2633217

Fixes: e4a668c ("carl9170: fix spurious restart due to high latency")
Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Acked-by: Christian Lamparter <chunkeey@gmail.com>
Link: https://patch.msgid.link/20250616181205.38883-1-dmantipov@yandex.ru
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>

Author: dmantipov

drivers/net/wireless/ath/carl9170/usb.c

@@ -438,14 +438,21 @@ static void carl9170_usb_rx_complete(struct urb *urb)
 
 		if (atomic_read(&ar->rx_anch_urbs) == 0) {
 			/*
-			 * The system is too slow to cope with
-			 * the enormous workload. We have simply
-			 * run out of active rx urbs and this
-			 * unfortunately leads to an unpredictable
-			 * device.
+			 * At this point, either the system is too slow to
+			 * cope with the enormous workload (so we have simply
+			 * run out of active rx urbs and this unfortunately
+			 * leads to an unpredictable device), or the device
+			 * is not fully functional after an unsuccessful
+			 * firmware loading attempts (so it doesn't pass
+			 * ieee80211_register_hw() and there is no internal
+			 * workqueue at all).
 			 */
 
-			ieee80211_queue_work(ar->hw, &ar->ping_work);
+			if (ar->registered)
+				ieee80211_queue_work(ar->hw, &ar->ping_work);
+			else
+				pr_warn_once("device %s is not registered\n",
+					     dev_name(&ar->udev->dev));
 		}
 	} else {
 		/*