If 'cpufreq_unregister_driver()' fails, just WARN and continue, so that
other resources are freed.

Fixes: de322e08 ("cpufreq: brcmstb-avs-cpufreq: AVS CPUfreq driver for Broadcom STB SoCs")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
[ Viresh: Updated Subject ]
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>