sata_mv: replace 0x1f with ATA_PIO4 (v2)

Cosmetic change: replace .pio_mask=0x1f with .pio_mask=ATA_PIO4 everywhere.
Originally from Erik Inge Bolsø, now reworked for latest sata_mv.

Signed-off-by: Erik Inge Bolsø <knan-lkml@anduin.net>
Signed-off-by: Mark Lord <mlord@pobox.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>