greybus: svc: always register interfaces at hotplug

Always register interfaces at hotplug regardless of whether
initialisation succeeded or not.

Even if a module failed to initialise we want it to have a
representation while it is physically present.

Note that the vendor and product-string attribute will read as "(null)"
for now on an interface that failed (early) initialisation.

Also note that the switch route is kept until the interface is finally
removed also on initialisation errors.

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