devlink: Release nested relation on devlink free

In the Linux kernel, the following vulnerability has been resolved: devlink: Release nested relation on devlink free devlink relation state is normally released from devl_unregister(), which calls devlink_rel_put(). This misses devlink instances that get a nested relation before registration and then fail probe before devl_register() is reached. That flow can happen for SFs. The child devlink gets linked to its parent before registration, then a later probe error calls devlink_free() directly. Since the instance was never registered, devl_unregister() is not called and devlink->rel is leaked. Release any pending relation from devlink_free() as well. The registered path is unchanged because devl_unregister() already clears devlink->rel before devlink_free() runs.