cpufreq: Don't check if cpu is online/offline for cpufreq callbacks

cpufreq layer doesn't call cpufreq driver's callback for any offline
CPU and so checking that isn't useful.

Lets get rid of it.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>