cpufreq: Detect spurious invocations of update_policy_cpu()

cpufreq: Detect spurious invocations of update_policy_cpu()

The function update_policy_cpu() is expected to be called when the policy->cpu
of a cpufreq policy is to be changed: ie., the new CPU nominated to become the
policy->cpu is different from the old one.

Print a warning if it is invoked with new_cpu == old_cpu, since such an
invocation might hint at a faulty logic in the caller.

Suggested-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>