use correct state_class for charging_power

[ronaldt80]

State class total is not correct for power entities - changed to measurement. This solves error message in HA log:

Entity sensor.wallbox_charging_power (<class 'homeassistant.components.mqtt.sensor.MqttSensor'>) is using state class 'total' which is impossible considering device class ('power') it is using; expected None or one of 'measurement'; 
Please update your configuration if your entity is manually configured, otherwise create a bug report at https://github.com/home-assistant/core/issues?q=is%3Aopen+is%3Aissue+label%3A%22integration%3A+mqtt%22

[jagheterfredrik]

Makes sense to me, thanks 👍