mcb: Use the actual bus passed to init and release functions

The functions mcb_bus_add_devices() and mcb_devices_unregister()
take a mcb_bus as argument that is never being used. This implies
that there is only one bus.

Do not ignore mcb_bus parameter and get the actual bus_type from
the device related to this mcb_bus.

Co-developed-by: Jorge Sanjuan Garcia <jorge.sanjuangarcia@duagon.com>
Signed-off-by: Jorge Sanjuan Garcia <jorge.sanjuangarcia@duagon.com>
Signed-off-by: Jose Javier Rodriguez Barbarin <JoseJavier.Rodriguez@duagon.com>
Link: https://lore.kernel.org/r/20231020124324.54692-2-JoseJavier.Rodriguez@duagon.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>