net: axienet: fix number of TX ring slots for available check

The check for the number of available TX ring slots was off by 1 since a
slot is required for the skb header as well as each fragment. This could
result in overwriting a TX ring slot that was still in use.

Fixes: 8a3b7a25 ("drivers/net/ethernet/xilinx: added Xilinx AXI Ethernet driver")
Signed-off-by: Robert Hancock <robert.hancock@calian.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/xilinx/xilinx_axienet_main.c

@@ -747,7 +747,7 @@ axienet_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 	num_frag = skb_shinfo(skb)->nr_frags;
 	cur_p = &lp->tx_bd_v[lp->tx_bd_tail];
 
-	if (axienet_check_tx_bd_space(lp, num_frag)) {
+	if (axienet_check_tx_bd_space(lp, num_frag + 1)) {
 		if (netif_queue_stopped(ndev))
 			return NETDEV_TX_BUSY;
 
@@ -757,7 +757,7 @@ axienet_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 		smp_mb();
 
 		/* Space might have just been freed - check again */
-		if (axienet_check_tx_bd_space(lp, num_frag))
+		if (axienet_check_tx_bd_space(lp, num_frag + 1))
 			return NETDEV_TX_BUSY;
 
 		netif_wake_queue(ndev);