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: NWei Yongjun <weiyongjun1@huawei.com>
Acked-by: NMarkus Mayer <mmayer@broadcom.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>