ath6kl: Fix lockdep warning

The following is the lockdep warning which detects possible
deadlock condition with the way ar->lock and ar->list_lock
are being used.

  (&(&ar->lock)->rlock){+.-...}, at: [<ffffffffa0492d13>] ath6kl_indicate_tx_activity+0x83/0x110 [ath6kl]
 but this lock took another, SOFTIRQ-unsafe lock in the past:
  (&(&ar->list_lock)->rlock){+.+...}

 and interrupts could create inverse lock ordering between them.

 other info that might help us debug this:
  Possible interrupt unsafe locking scenario:

        CPU0                    CPU1
        ----                    ----
   lock(&(&ar->list_lock)->rlock);
                                local_irq_disable();
                                lock(&(&ar->lock)->rlock);
                                lock(&(&ar->list_lock)->rlock);
   <Interrupt>
     lock(&(&ar->lock)->rlock);

  *** DEADLOCK ***

softirqs have to be disabled when acquiring ar->list_lock to avoid
the above deadlock condition. When the above warning printed the
interface is still up and running without issue.

Reported-by: Kalle Valo <kvalo@qca.qualcomm.com>
Signed-off-by: Vasanthakumar Thiagarajan <vthiagar@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>

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

@@ -1046,15 +1046,15 @@ struct ath6kl_vif *ath6kl_vif_first(struct ath6kl *ar)
 {
 	struct ath6kl_vif *vif;
 
-	spin_lock(&ar->list_lock);
+	spin_lock_bh(&ar->list_lock);
 	if (list_empty(&ar->vif_list)) {
-		spin_unlock(&ar->list_lock);
+		spin_unlock_bh(&ar->list_lock);
 		return NULL;
 	}
 
 	vif = list_first_entry(&ar->vif_list, struct ath6kl_vif, list);
 
-	spin_unlock(&ar->list_lock);
+	spin_unlock_bh(&ar->list_lock);
 
 	return vif;
 }