Fix bug in ofwbus_release_resource() for non-ofwbus descendants

[zbb]

Summary

Resource list for devices that are not ofwbus descendants, but
got to ofwbus method via bus_generic_release_resource() call chain,
cannot be found using BUS_GET_RESOURCE_LIST() used by ofwbus.
In that case, changing device's resource list should be avoided
(will not contain resource list prepared by ofw or simplebus).