cpufreq: brcmstb-avs: fix imbalance of cpufreq policy refcount

brcm_avs_cpufreq_get() calls cpufreq_cpu_get() to get the cpufreq
policy, meanwhile, it also increments the kobject reference count
to mark it busy. However, a corresponding call of cpufreq_cpu_put()
is ignored to decrement the kobject reference count back, which may
lead to a potential stuck risk that the cpuhp thread deadly waits
for dropping of kobject refcount when cpufreq policy free.

With this patch, the cpuhp thread can be easily exercised by
attempting to force an unbind of the CPUfreq driver.

Signed-off-by: chenqiwu <chenqiwu@xiaomi.com>
[ Viresh: Dropped !policy check ]
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>