driver core: bus: bus_get_kset() cleanup

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

Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Link: https://lore.kernel.org/r/20230208111330.439504-10-gregkh@linuxfoundation.org


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