pata_mpc52xx: inherit from ata_bmdma_port_ops

pata_mpc52xx supports BMDMA but inherits ata_sff_port_ops which
triggers BUG_ON() when a DMA command is issued.  Fix it.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Roman Fietze <roman.fietze@telemotive.de>
Cc: Sergei Shtylyov <sshtylyov@mvista.com>
Cc: stable@kernel.org
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>