cpufreq: apple-soc: Fix null-ptr-deref in apple_soc_cpufreq_get_rate()

cpufreq_cpu_get_raw() can return NULL when the target CPU is not present
in the policy->cpus mask. apple_soc_cpufreq_get_rate() does not check
for this case, which results in a NULL pointer dereference.

Fixes: 6286bbb ("cpufreq: apple-soc: Add new driver to control Apple SoC CPU P-states")
Signed-off-by: Henry Martin <bsdhenrymartin@gmail.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

Author: Henry Martin

drivers/cpufreq/apple-soc-cpufreq.c

@@ -134,11 +134,17 @@ static const struct of_device_id apple_soc_cpufreq_of_match[] __maybe_unused = {
 
 static unsigned int apple_soc_cpufreq_get_rate(unsigned int cpu)
 {
-	struct cpufreq_policy *policy = cpufreq_cpu_get_raw(cpu);
-	struct apple_cpu_priv *priv = policy->driver_data;
+	struct cpufreq_policy *policy;
+	struct apple_cpu_priv *priv;
 	struct cpufreq_frequency_table *p;
 	unsigned int pstate;
 
+	policy = cpufreq_cpu_get_raw(cpu);
+	if (unlikely(!policy))
+		return 0;
+
+	priv = policy->driver_data;
+
 	if (priv->info->cur_pstate_mask) {
 		u32 reg = readl_relaxed(priv->reg_base + APPLE_DVFS_STATUS);