greybus: control: do not assume a control bundle

The control bundle is going away so update the code.

Also remove defensive WARN_ON which would not just warn if our
implementation is broken, but also leak further memory unnecessarily.

Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>