qemu: hotplug: fix mdev attach for vfio-ccw
    
    Mediated devices of model 'vfio-ccw' are using CCW addresses, so make
    sure to call the correct address preparation code for the model.
    
    Reviewed-by: Shalini Chellathurai Saroja <shalini@linux.ibm.com>
    Reviewed-by: Boris Fiuczynski <fiuczy@linux.ibm.com>
    Signed-off-by: Bjoern Walk <bwalk@linux.ibm.com>
    Reviewed-by: John Ferlan <jferlan@redhat.com>