mcb: Correctly initialize the bus's device

The mcb bus' device member wasn't correctly initialized and thus wasn't placed
correctly into the driver model.

Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Andreas Werner <andreas.werner@men.de>
Tested-by: Andreas Werner <andreas.werner@men.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>