ath6kl: avoid flush_scheduled_work() usage

As per commit c4f135d6 ("workqueue: Wrap flush_workqueue() using
a macro") says, use per "struct ath6kl_usb" workqueue.

This is a blind conversion, and is only compile tested.
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/f78ddbdc-8989-a1a7-2234-ce9ec3894625@I-love.SAKURA.ne.jp

drivers/net/wireless/ath/ath6kl/usb.c

@@ -71,6 +71,7 @@ struct ath6kl_usb {
 	u8 *diag_cmd_buffer;
 	u8 *diag_resp_buffer;
 	struct ath6kl *ar;
+	struct workqueue_struct *wq;
 };
 
 /* usb urb object */
@@ -478,7 +479,7 @@ static void ath6kl_usb_flush_all(struct ath6kl_usb *ar_usb)
 	 * Flushing any pending I/O may schedule work this call will block
 	 * until all scheduled work runs to completion.
 	 */
-	flush_scheduled_work();
+	flush_workqueue(ar_usb->wq);
 }
 
 static void ath6kl_usb_start_recv_pipes(struct ath6kl_usb *ar_usb)
@@ -544,7 +545,7 @@ static void ath6kl_usb_recv_complete(struct urb *urb)
 
 	/* note: queue implements a lock */
 	skb_queue_tail(&pipe->io_comp_queue, skb);
-	schedule_work(&pipe->io_complete_work);
+	queue_work(pipe->ar_usb->wq, &pipe->io_complete_work);
 
 cleanup_recv_urb:
 	ath6kl_usb_cleanup_recv_urb(urb_context);
@@ -579,7 +580,7 @@ static void ath6kl_usb_usb_transmit_complete(struct urb *urb)
 
 	/* note: queue implements a lock */
 	skb_queue_tail(&pipe->io_comp_queue, skb);
-	schedule_work(&pipe->io_complete_work);
+	queue_work(pipe->ar_usb->wq, &pipe->io_complete_work);
 }
 
 static void ath6kl_usb_io_comp_work(struct work_struct *work)
@@ -619,6 +620,7 @@ static void ath6kl_usb_destroy(struct ath6kl_usb *ar_usb)
 
 	kfree(ar_usb->diag_cmd_buffer);
 	kfree(ar_usb->diag_resp_buffer);
+	destroy_workqueue(ar_usb->wq);
 
 	kfree(ar_usb);
 }
@@ -631,9 +633,15 @@ static struct ath6kl_usb *ath6kl_usb_create(struct usb_interface *interface)
 	int status = 0;
 	int i;
 
+	/* ath6kl_usb_destroy() needs ar_usb != NULL && ar_usb->wq != NULL. */
 	ar_usb = kzalloc(sizeof(struct ath6kl_usb), GFP_KERNEL);
 	if (ar_usb == NULL)
-		goto fail_ath6kl_usb_create;
+		return NULL;
+	ar_usb->wq = alloc_workqueue("ath6kl_wq", 0, 0);
+	if (!ar_usb->wq) {
+		kfree(ar_usb);
+		return NULL;
+	}
 
 	usb_set_intfdata(interface, ar_usb);
 	spin_lock_init(&(ar_usb->cs_lock));