cpufreq: amd-pstate: add check for cpufreq_cpu_get's return value

cpufreq_cpu_get may return NULL. To avoid NULL-dereference check it
and return in case of error.

Found by Linux Verification Center (linuxtesting.org) with SVACE.
Signed-off-by: Anastasia Belova <abelova@astralinux.ru>
Reviewed-by: Perry Yuan <perry.yuan@amd.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

drivers/cpufreq/amd-pstate.c

@@ -659,7 +659,12 @@ static void amd_pstate_adjust_perf(unsigned int cpu,
 	unsigned long max_perf, min_perf, des_perf,
 		      cap_perf, lowest_nonlinear_perf;
 	struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
-	struct amd_cpudata *cpudata = policy->driver_data;
+	struct amd_cpudata *cpudata;
+
+	if (!policy)
+		return;
+
+	cpudata = policy->driver_data;
 
 	if (policy->min != cpudata->min_limit_freq || policy->max != cpudata->max_limit_freq)
 		amd_pstate_update_min_max_limit(policy);
@@ -873,11 +878,16 @@ static void amd_pstate_init_prefcore(struct amd_cpudata *cpudata)
 static void amd_pstate_update_limits(unsigned int cpu)
 {
 	struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
-	struct amd_cpudata *cpudata = policy->driver_data;
+	struct amd_cpudata *cpudata;
 	u32 prev_high = 0, cur_high = 0;
 	int ret;
 	bool highest_perf_changed = false;
 
+	if (!policy)
+		return;
+
+	cpudata = policy->driver_data;
+
 	mutex_lock(&amd_pstate_driver_lock);
 	if ((!amd_pstate_prefcore) || (!cpudata->hw_prefcore))
 		goto free_cpufreq_put;