PM / QoS: Fix the return value of dev_pm_qos_update_request()

Commit e39473d0 (PM / QoS: Make it possible to expose PM QoS device
flags to user space) introduced __dev_pm_qos_update_request() to be
called internally by dev_pm_qos_update_request(), but forgot to make
the latter actually use the return value of the former.  Fix this
mistake.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/base/power/qos.c

@@ -380,7 +380,7 @@ int dev_pm_qos_update_request(struct dev_pm_qos_request *req, s32 new_value)
 		return -EINVAL;
 
 	mutex_lock(&dev_pm_qos_mtx);
-	__dev_pm_qos_update_request(req, new_value);
+	ret = __dev_pm_qos_update_request(req, new_value);
 	mutex_unlock(&dev_pm_qos_mtx);
 
 	return ret;