driver core: bus: clean up bus_sort_breadthfirst()

Convert the bus_sort_breadthfirst() function to use bus_to_subsys() and
not use the back-pointer to the private structure.

This also allows us to get rid of bus_get_device_klist() which was only
being used by this one internal function.

Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Link: https://lore.kernel.org/r/20230208111330.439504-14-gregkh@linuxfoundation.org


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