net: hisilicon: fix handling platform_get_irq result

The function can return negative value.

The problem has been detected using proposed semantic patch
scripts/coccinelle/tests/assign_signed_to_unsigned.cocci [1].

[1]: http://permalink.gmane.org/gmane.linux.kernel/2046107

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/hisilicon/hip04_eth.c

@@ -816,7 +816,7 @@ static int hip04_mac_probe(struct platform_device *pdev)
 	struct net_device *ndev;
 	struct hip04_priv *priv;
 	struct resource *res;
-	unsigned int irq;
+	int irq;
 	int ret;
 
 	ndev = alloc_etherdev(sizeof(struct hip04_priv));