greybus: core: fix hd-creation error path

Make sure to return an errno when a host-device buffer-size check fails.

Fixes: 1f92f6404614 ("core: return error code when creating host device")
Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>