Using a standard QOM object link we can pass a reference to the MAC_DBDMA
controller to the MACIO_IDE object which removes the last external parameter
to macio_ide_register_dma().

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>