driver core: bus: subsys_interface_register/unregister() cleanups

Convert the subsys_interface_register and subsys_interface_unregister()
functions to use bus_to_subsys() and not use the back-pointer to the
private structure.

This also requires changing the parameters on subsys_dev_iter_init() to
iterate over the list properly.

Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Link: https://lore.kernel.org/r/20230208111330.439504-9-gregkh@linuxfoundation.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>