thermal: Fix locking in cooling device sysfs update cur_state

Sysfs interface to update cooling device cur_state does not
currently holding cooling device lock sometimes leading to
stale values in cur_state if getting updated simultanelously
from user space and thermal framework. Adding the proper locking
code fixes this issue.
Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>

drivers/thermal/thermal_sysfs.c

@@ -712,11 +712,14 @@ cur_state_store(struct device *dev, struct device_attribute *attr,
 	if ((long)state < 0)
 		return -EINVAL;
 
+	mutex_lock(&cdev->lock);
+
 	result = cdev->ops->set_cur_state(cdev, state);
-	if (result)
-		return result;
+	if (!result)
 		thermal_cooling_device_stats_update(cdev, state);
-	return count;
+
+	mutex_unlock(&cdev->lock);
+	return result ? result : count;
 }
 
 static struct device_attribute