staging: vt6655: device_free_tx_buf use only ieee80211_tx_status_irqsafe

TD_FLAGS_NETIF_SKB is only for data.

Fixes issue of ack frames not being reported.
Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Cc: <stable@vger.kernel.org> # v3.19+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vt6655/device_main.c

@@ -989,10 +989,8 @@ static void device_free_tx_buf(struct vnt_private *pDevice, PSTxDesc pDesc)
 				 skb->len, DMA_TO_DEVICE);
 	}
 
-	if (pTDInfo->byFlags & TD_FLAGS_NETIF_SKB)
+	if (skb)
 		ieee80211_tx_status_irqsafe(pDevice->hw, skb);
-	else
-		dev_kfree_skb_irq(skb);
 
 	pTDInfo->skb_dma = 0;
 	pTDInfo->skb = NULL;