sata_promise: fix 20619 new EH merge error

When I merged my 20619 new EH conversion with #libata-upstream
I had to manually resolve a conflict, and inadvertently lost
pdc_pata_ops' ->post_internal_cmd binding. Corrected by this patch.

Signed-off-by: Mikael Pettersson <mikpe@it.uu.se>
Signed-off-by: Jeff Garzik <jeff@garzik.org>