itech-it8500: rephrase config get/set/list, reflect error paths

itech-it8500: rephrase config get/set/list, reflect error paths

Explicitly "break the flow" when internal status gathering fails, to
reflect that an error path is taken and the config call will fail. The
conditional assignment of response data in case of success could be
slightly misleading (it was to me during review).

Eliminate a goto which kind of circumvented the optional transmission of
a request to the device. Instead test whether a command was filled in to
determine whether a command needs to get sent.