libata-core: auditting chk_status v check_status

Did a complete audit of these and found we have another error case.

ata_bus_softreset calls ata_check_status which means that it tries to do
an ioread8 on the port blindly and check versus 0xFF for an error.

It should of course be using the ap->ops method for this via chk_status,
and this bug causes a wrog status call on the NS87415 at least.

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>