lib82596: Fix IRQ check in sni_82596_probe

platform_get_irq() returns negative error number instead 0 on failure.
And the doc of platform_get_irq() provides a usage example:

    int irq = platform_get_irq(pdev, 0);
    if (irq < 0)
        return irq;

Fix the check of return value to catch errors correctly.

Fixes: 11597885 ("i825xx: Move the Intel 82586/82593/82596 based drivers")
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/i825xx/sni_82596.c

@@ -117,9 +117,10 @@ static int sni_82596_probe(struct platform_device *dev)
 	netdevice->dev_addr[5] = readb(eth_addr + 0x06);
 	iounmap(eth_addr);
 
-	if (!netdevice->irq) {
+	if (netdevice->irq < 0) {
 		printk(KERN_ERR "%s: IRQ not found for i82596 at 0x%lx\n",
 			__FILE__, netdevice->base_addr);
+		retval = netdevice->irq;
 		goto probe_failed;
 	}