gianfar: Do right check on num_txbdfree

This patch fixes a wrong check on num_txbdfree. It could lead to
num_txbdfree become nagative.  Result was that the gianfar stops
sending data.

Changes from first version :
- removed a space between parens (David Millers comment)
- full email address in signed off line
Signed-off-by: Rini van Zetten <rini@arvoo.nl>
Acked-by: Andy Fleming <afleming@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/gianfar.c

@@ -1284,7 +1284,7 @@ static int gfar_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	spin_lock_irqsave(&priv->txlock, flags);
 
 	/* check if there is space to queue this packet */
-	if (nr_frags > priv->num_txbdfree) {
+	if ((nr_frags+1) > priv->num_txbdfree) {
 		/* no space, stop the queue */
 		netif_stop_queue(dev);
 		dev->stats.tx_fifo_errors++;