sata_nv: use ata_pci_sff_activate_host() instead of ata_host_activate()

sata_nv was incorrectly using ata_host_activate() instead of
ata_pci_sff_activate_host() leading to IRQ assignment failure in
legacy mode.  Fix it.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Robert Hancock <hancockr@shaw.ca>
Cc: stable@kernel.org
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>