thermal: exynos_thermal: return a proper error code while thermal_zone_device_register fail.

we are returning EINVAL while the thermal_zone_device_register function fail.
instead we can use the return value from the thermal_zone_device_register by
using PTR_ERR.
Signed-off-by: Devendra Naga <devendra.aaru@gmail.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>

drivers/thermal/exynos_thermal.c

@@ -476,7 +476,7 @@ static int exynos_register_thermal(struct thermal_sensor_conf *sensor_conf)
 
 	if (IS_ERR(th_zone->therm_dev)) {
 		pr_err("Failed to register thermal zone device\n");
-		ret = -EINVAL;
+		ret = PTR_ERR(th_zone->therm_dev);
 		goto err_unregister;
 	}
 	th_zone->mode = THERMAL_DEVICE_ENABLED;