thermal: cpu_cooling: update documentation for cpufreq_set_cur_state

Update documentation for cpufreq_set_cur_state callback.
Signed-off-by: NEduardo Valentin <eduardo.valentin@ti.com>
Acked-by: NAmit Daniel Kachhap <amit.daniel@samsung.com>
Signed-off-by: NZhang Rui <rui.zhang@intel.com>

drivers/thermal/cpu_cooling.c

@@ -384,6 +384,11 @@ static int cpufreq_get_cur_state(struct thermal_cooling_device *cdev,
  * cpufreq_set_cur_state - callback function to set the current cooling state.
  * @cdev: thermal cooling device pointer.
  * @state: set this variable to the current cooling state.
+ *
+ * Callback for the thermal cooling device to change the cpufreq
+ * current cooling state.
+ *
+ * Return: 0 on success, an error code otherwise.
  */
 static int cpufreq_set_cur_state(struct thermal_cooling_device *cdev,
 				 unsigned long state)