PM / Domains: Fix return value of of_genpd_opp_to_performance_state()

of_genpd_opp_to_performance_state() should return 0 for errors, but the
dummy routine isn't doing that. Fix it.
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

include/linux/pm_domain.h

@@ -276,7 +276,7 @@ static inline unsigned int
 of_genpd_opp_to_performance_state(struct device *dev,
 				  struct device_node *opp_node)
 {
-	return -ENODEV;
+	return 0;
 }
 
 static inline int genpd_dev_pm_attach(struct device *dev)