ARM: OMAP: fix return value check in omap_device_build_from_dt()

In case of error, the function omap_device_alloc() returns ERR_PTR()
and never returns NULL. The NULL test in the return value check
should be replaced with IS_ERR().
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Acked-by: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/mach-omap2/omap_device.c

@@ -158,7 +158,7 @@ static int omap_device_build_from_dt(struct platform_device *pdev)
 	}
 
 	od = omap_device_alloc(pdev, hwmods, oh_cnt);
-	if (!od) {
+	if (IS_ERR(od)) {
 		dev_err(&pdev->dev, "Cannot allocate omap_device for :%s\n",
 			oh_name);
 		ret = PTR_ERR(od);