ibm_newemac: Fixes kernel crashes when speed of cable connected changes

The descriptor pointers were not initialized to NIL values, so it was
poiniting to some random addresses which was completely invalid. This
fix takes care of initializing the descriptor to NIL values and clearing
the valid descriptors on clean ring operation.

Signed-off-by: Sathya Narayanan <sathyan@teamf1.com>
Signed-off-by: Stefan Roese <sr@denx.de>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/net/ibm_newemac/core.c

@@ -2719,6 +2719,8 @@ static int __devinit emac_probe(struct of_device *ofdev,
 	/* Clean rings */
 	memset(dev->tx_desc, 0, NUM_TX_BUFF * sizeof(struct mal_descriptor));
 	memset(dev->rx_desc, 0, NUM_RX_BUFF * sizeof(struct mal_descriptor));
+	memset(dev->tx_skb, 0, NUM_TX_BUFF * sizeof(struct sk_buff *));
+	memset(dev->rx_skb, 0, NUM_RX_BUFF * sizeof(struct sk_buff *));
 
 	/* Attach to ZMII, if needed */
 	if (emac_has_feature(dev, EMAC_FTR_HAS_ZMII) &&