cpufreq: brcmstb-avs-cpufreq: make symbol brcm_avs_cpufreq_attr static

Fixes the following sparse warning:

drivers/cpufreq/brcmstb-avs-cpufreq.c:982:18: warning:
 symbol 'brcm_avs_cpufreq_attr' was not declared. Should it be static?
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Markus Mayer <mmayer@broadcom.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/brcmstb-avs-cpufreq.c

@@ -979,7 +979,7 @@ cpufreq_freq_attr_ro(brcm_avs_pmap);
 cpufreq_freq_attr_ro(brcm_avs_voltage);
 cpufreq_freq_attr_ro(brcm_avs_frequency);
 
-struct freq_attr *brcm_avs_cpufreq_attr[] = {
+static struct freq_attr *brcm_avs_cpufreq_attr[] = {
 	&cpufreq_freq_attr_scaling_available_freqs,
 	&brcm_avs_pstate,
 	&brcm_avs_mode,