greybus: connection: use bundle device for bundle error messages

It is safe to use the bundle device for error messages when we know we
have a bundle.

Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>