net: stmmac: Fixed the condition of extend_desc for jumbo frame

This patch fixed the condition of extend_desc for jumbo frame.
There is no check routine for extend_desc in the stmmac_jumbo_frm function.
Even though extend_desc is set if dma_tx is used instead of dma_etx.
It causes kernel panic.
Signed-off-by: Byungho An <bh74.an@samsung.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/ring_mode.c

@@ -33,10 +33,15 @@ static unsigned int stmmac_jumbo_frm(void *p, struct sk_buff *skb, int csum)
 	struct stmmac_priv *priv = (struct stmmac_priv *)p;
 	unsigned int txsize = priv->dma_tx_size;
 	unsigned int entry = priv->cur_tx % txsize;
-	struct dma_desc *desc = priv->dma_tx + entry;
+	struct dma_desc *desc;
 	unsigned int nopaged_len = skb_headlen(skb);
 	unsigned int bmax, len;
 
+	if (priv->extend_desc)
+		desc = (struct dma_desc *)(priv->dma_etx + entry);
+	else
+		desc = priv->dma_tx + entry;
+
 	if (priv->plat->enh_desc)
 		bmax = BUF_SIZE_8KiB;
 	else
@@ -54,6 +59,10 @@ static unsigned int stmmac_jumbo_frm(void *p, struct sk_buff *skb, int csum)
 						STMMAC_RING_MODE);
 		wmb();
 		entry = (++priv->cur_tx) % txsize;
+
+		if (priv->extend_desc)
+			desc = (struct dma_desc *)(priv->dma_etx + entry);
+		else
 			desc = priv->dma_tx + entry;
 
 		desc->des2 = dma_map_single(priv->device, skb->data + bmax,