cpufreq: qcom-hw: Fix return value check in qcom_cpufreq_hw_cpu_init()

In case of error, the function ioremap() returns NULL pointer
not ERR_PTR(). The IS_ERR() test in the return value check
should be replaced with NULL test.

Fixes: 67fc209b

 ("cpufreq: qcom-hw: drop devm_xxx() calls from init/exit hooks")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>