ARM: OMAP3: Beagle: fix return value check in beagle_opp_init()

In case of error, the function get_cpu_device() returns NULL pointer
not ERR_PTR(). The IS_ERR() test in the return value check should be
replaced with NULL test.
Signed-off-by: NWei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: NTony Lindgren <tony@atomide.com>

arch/arm/mach-omap2/board-omap3beagle.c

@@ -510,7 +510,7 @@ static int __init beagle_opp_init(void)
 		mpu_dev = get_cpu_device(0);
 		iva_dev = omap_device_get_by_hwmod_name("iva");
 
-		if (IS_ERR(mpu_dev) || IS_ERR(iva_dev)) {
+		if (!mpu_dev || IS_ERR(iva_dev)) {
 			pr_err("%s: Aiee.. no mpu/dsp devices? %p %p\n",
 				__func__, mpu_dev, iva_dev);
 			return -ENODEV;