PM / devfreq: Fix compiler warnings for CONFIG_PM_DEVFREQ unset

Fix compiler warnings generated when devfreq is not enabled
(CONFIG_PM_DEVFREQ is not set).

Signed-off-by: Rajagopal Venkat <rajagopal.venkat@linaro.org>
Acked-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

include/linux/devfreq.h

@@ -213,42 +213,42 @@ struct devfreq_simple_ondemand_data {
 #endif
 
 #else /* !CONFIG_PM_DEVFREQ */
-static struct devfreq *devfreq_add_device(struct device *dev,
+static inline struct devfreq *devfreq_add_device(struct device *dev,
 					  struct devfreq_dev_profile *profile,
 					  const char *governor_name,
 					  void *data)
 {
 	return NULL;
 }
 
-static int devfreq_remove_device(struct devfreq *devfreq)
+static inline int devfreq_remove_device(struct devfreq *devfreq)
 {
 	return 0;
 }
 
-static int devfreq_suspend_device(struct devfreq *devfreq)
+static inline int devfreq_suspend_device(struct devfreq *devfreq)
 {
 	return 0;
 }
 
-static int devfreq_resume_device(struct devfreq *devfreq)
+static inline int devfreq_resume_device(struct devfreq *devfreq)
 {
 	return 0;
 }
 
-static struct opp *devfreq_recommended_opp(struct device *dev,
+static inline struct opp *devfreq_recommended_opp(struct device *dev,
 					   unsigned long *freq, u32 flags)
 {
-	return -EINVAL;
+	return ERR_PTR(-EINVAL);
 }
 
-static int devfreq_register_opp_notifier(struct device *dev,
+static inline int devfreq_register_opp_notifier(struct device *dev,
 					 struct devfreq *devfreq)
 {
 	return -EINVAL;
 }
 
-static int devfreq_unregister_opp_notifier(struct device *dev,
+static inline int devfreq_unregister_opp_notifier(struct device *dev,
 					   struct devfreq *devfreq)
 {
 	return -EINVAL;