cpufreq: Avoid false-positive WARN_ON()s in cpufreq_update_policy()

commit 742c87bf upstream.

CPU notifications from the firmware coming in when cpufreq is
suspended cause cpufreq_update_current_freq() to return 0 which
triggers the WARN_ON() in cpufreq_update_policy() for no reason.

Avoid that by checking cpufreq_suspended before calling
cpufreq_update_current_freq().

Fixes: c9d9c929 (cpufreq: Abort cpufreq_update_current_freq() for cpufreq_suspended set)
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>