sata_promise: simplify port setup

Each place in pdc_ata_init_one() that initialises a SATA
port first calls pdc_ata_setup_port(), and then manually
assigns the port's ->scr_addr. Simplify the code by extending
pdc_ata_setup_port() to also handle scr_addr initialisation;
for PATA ports we pass NULL as scr_addr.

The initialisation of the PATA-only 20619 redundantly set
up scr_addr for the ports. Remove this.

Tested on 20619, 20575, and 20775 chips.

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