greybus: connection: fix potential null-deref in hd_cport_enable

Use parent of host device for error messages as the connections bundle
may be NULL.

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>