PM: domains: Return early if perf state is already set for the device

When dev_pm_genpd_set_performance_state() gets called to set a new
performance state for the device, let's take a quicker path by doing an
early return, if it turns out that the new state is already set for the
device.
Suggested-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/base/power/domain.c

@@ -387,6 +387,9 @@ static int genpd_set_performance_state(struct device *dev, unsigned int state)
 	int ret;
 
 	prev_state = gpd_data->performance_state;
+	if (prev_state == state)
+		return 0;
+
 	gpd_data->performance_state = state;
 	state = _genpd_reeval_performance_state(genpd, state);