powerpc/mv643xx_eth: fix return check in mv64x60_eth_register_shared_pdev()

In case of error, the function platform_device_register_simple() returns
RR_PTR() and never returns NULL. The NULL test in the return value check
should be replaced with IS_ERR().
Signed-off-by: NWei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: NScott Wood <scottwood@freescale.com>

arch/powerpc/sysdev/mv64x60_dev.c

@@ -228,7 +228,7 @@ static struct platform_device * __init mv64x60_eth_register_shared_pdev(
 
 	if (id == 0) {
 		pdev = platform_device_register_simple("orion-mdio", -1, &r[1], 1);
-		if (!pdev)
+		if (IS_ERR(pdev))
 			return pdev;
 	}