cpufreq: ap806: Add NULL check after kcalloc

Add NULL check  after kcalloc.

Fix below issue reported by coccicheck
./drivers/cpufreq/armada-8k-cpufreq.c:138:1-12: alloc with no test,
possible model on line 151
Signed-off-by: Hariprasad Kelam <hariprasad.kelam@gmail.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

drivers/cpufreq/armada-8k-cpufreq.c

@@ -136,6 +136,8 @@ static int __init armada_8k_cpufreq_init(void)
 
 	nb_cpus = num_possible_cpus();
 	freq_tables = kcalloc(nb_cpus, sizeof(*freq_tables), GFP_KERNEL);
+	if (!freq_tables)
+		return -ENOMEM;
 	cpumask_copy(&cpus, cpu_possible_mask);
 
 	/*