1. the args on the launch file, do not have the correct name. You should specify there the name of the controller you defined in the config file, that is mobile_base_controller
2. also in the launch file, you are indicating a namespace /robot but that is not included in the yaml file. You can get rid of it
Those two points should resolved the problem of controller spawner couldn't .... However, you may have later a problem loading the controller with a different error report.