wifi: iwl4965: Add missing check for create_singlethread_workqueue()

Add the check for the return value of the create_singlethread_workqueue()
in order to avoid NULL pointer dereference.

Fixes: b481de9c ("[IWLWIFI]: add iwlwifi wireless drivers")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
Acked-by: Stanislaw Gruszka <stf_xl@wp.pl>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230209010748.45454-1-jiasheng@iscas.ac.cn

drivers/net/wireless/intel/iwlegacy/4965-mac.c

@@ -6211,10 +6211,12 @@ il4965_bg_txpower_work(struct work_struct *work)
 	mutex_unlock(&il->mutex);
 }
 
-static void
+static int
 il4965_setup_deferred_work(struct il_priv *il)
 {
 	il->workqueue = create_singlethread_workqueue(DRV_NAME);
+	if (!il->workqueue)
+		return -ENOMEM;
 
 	init_waitqueue_head(&il->wait_command_queue);
 
@@ -6233,6 +6235,8 @@ il4965_setup_deferred_work(struct il_priv *il)
 	timer_setup(&il->watchdog, il_bg_watchdog, 0);
 
 	tasklet_setup(&il->irq_tasklet, il4965_irq_tasklet);
+
+	return 0;
 }
 
 static void
@@ -6618,7 +6622,10 @@ il4965_pci_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 		goto out_disable_msi;
 	}
 
-	il4965_setup_deferred_work(il);
+	err = il4965_setup_deferred_work(il);
+	if (err)
+		goto out_free_irq;
+
 	il4965_setup_handlers(il);
 
 	/*********************************************
@@ -6656,6 +6663,7 @@ il4965_pci_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 out_destroy_workqueue:
 	destroy_workqueue(il->workqueue);
 	il->workqueue = NULL;
+out_free_irq:
 	free_irq(il->pci_dev->irq, il);
 out_disable_msi:
 	pci_disable_msi(il->pci_dev);