imx6q-cpufreq: fix return value check in imx6q_cpufreq_probe()

In case of error, the function devm_regulator_get() 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: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/imx6q-cpufreq.c

@@ -245,7 +245,7 @@ static int imx6q_cpufreq_probe(struct platform_device *pdev)
 	arm_reg = devm_regulator_get(cpu_dev, "arm");
 	pu_reg = devm_regulator_get(cpu_dev, "pu");
 	soc_reg = devm_regulator_get(cpu_dev, "soc");
-	if (!arm_reg || !pu_reg || !soc_reg) {
+	if (IS_ERR(arm_reg) || IS_ERR(pu_reg) || IS_ERR(soc_reg)) {
 		dev_err(cpu_dev, "failed to get regulators\n");
 		ret = -ENOENT;
 		goto put_node;