driver core: bus: bus_register/unregister() cleanups

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

Because bus_add_groups() and bus_remove_groups() were only called in one
place, remove those one-line-wrapper functions and call the real sysfs
group function where it is needed instead, saving another layer of
indirection.

Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Link: https://lore.kernel.org/r/20230208111330.439504-8-gregkh@linuxfoundation.org


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