rrunner: fix buffer overflow

tx_skbuff is define as:
        struct sk_buff          *tx_skbuff[TX_RING_ENTRIES];

EVT_RING_ENTRIES is 64 and TX_RING_ENTRIES is 32.

This function is in a error path so that's why it wasn't noticed.
Signed-off-by: NDan Carpenter <error27@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/rrunner.c

@@ -1293,7 +1293,7 @@ static void rr_dump(struct net_device *dev)
 
 	printk("Error code 0x%x\n", readl(&regs->Fail1));
 
-	index = (((readl(&regs->EvtPrd) >> 8) & 0xff ) - 1) % EVT_RING_ENTRIES;
+	index = (((readl(&regs->EvtPrd) >> 8) & 0xff) - 1) % TX_RING_ENTRIES;
 	cons = rrpriv->dirty_tx;
 	printk("TX ring index %i, TX consumer %i\n",
 	       index, cons);