staging: vt6655: dead code tx path remove dma_unmap_single

When pTDInfo->skb_dma not equal to pTDInfo->buf_dma, pTDInfo->skb_dma
equals zero.

as mentioned in comment pre-allocated buf_dma can't be unmapped
so remove dead code.
Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vt6655/device_main.c

@@ -754,10 +754,6 @@ static void device_free_td0_ring(struct vnt_private *pDevice)
 		PSTxDesc        pDesc = &(pDevice->apTD0Rings[i]);
 		PDEVICE_TD_INFO  pTDInfo = pDesc->pTDInfo;
 
-		if (pTDInfo->skb_dma && (pTDInfo->skb_dma != pTDInfo->buf_dma))
-			dma_unmap_single(&pDevice->pcid->dev, pTDInfo->skb_dma,
-					 pTDInfo->skb->len, DMA_TO_DEVICE);
-
 		dev_kfree_skb(pTDInfo->skb);
 		kfree(pDesc->pTDInfo);
 	}
@@ -771,10 +767,6 @@ static void device_free_td1_ring(struct vnt_private *pDevice)
 		PSTxDesc        pDesc = &(pDevice->apTD1Rings[i]);
 		PDEVICE_TD_INFO  pTDInfo = pDesc->pTDInfo;
 
-		if (pTDInfo->skb_dma && (pTDInfo->skb_dma != pTDInfo->buf_dma))
-			dma_unmap_single(&pDevice->pcid->dev, pTDInfo->skb_dma,
-					 pTDInfo->skb->len, DMA_TO_DEVICE);
-
 		dev_kfree_skb(pTDInfo->skb);
 		kfree(pDesc->pTDInfo);
 	}
@@ -975,12 +967,6 @@ static void device_free_tx_buf(struct vnt_private *pDevice, PSTxDesc pDesc)
 	PDEVICE_TD_INFO  pTDInfo = pDesc->pTDInfo;
 	struct sk_buff *skb = pTDInfo->skb;
 
-	/* pre-allocated buf_dma can't be unmapped. */
-	if (pTDInfo->skb_dma && (pTDInfo->skb_dma != pTDInfo->buf_dma)) {
-		dma_unmap_single(&pDevice->pcid->dev, pTDInfo->skb_dma,
-				 skb->len, DMA_TO_DEVICE);
-	}
-
 	if (skb)
 		ieee80211_tx_status_irqsafe(pDevice->hw, skb);