driver core: remove private pointer from struct bus_type

Now that the driver code has been refactored to not rely on the pointer
from a struct bus_type to the private structure it can be safely removed
from the structure entirely.

This will allow most bus_type structures to now be marked as const.

Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Link: https://lore.kernel.org/r/20230208111330.439504-18-gregkh@linuxfoundation.org


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