tg3: Avoid NULL pointer dereference in netif_device_attach()

Similar to commit<1b0ff89852d7>("tg3: Avoid NULL pointer dereference in tg3_io_error_detected()")
This patch avoids NULL pointer dereference add a check for netdev being NULL on tg3_resume().

Signed-off-by: Defang Bo <bodefang@126.com>

drivers/net/ethernet/broadcom/tg3.c

@@ -18108,7 +18108,7 @@ static int tg3_resume(struct device *device)
 
 	rtnl_lock();
 
-	if (!netif_running(dev))
+	if (!netdev || !netif_running(dev))
 		goto unlock;
 
 	netif_device_attach(dev);