libata-sff: Correct use of check_status()

ata_check_status() does an SFF compliant check
ata_chk_status() does a generic call to ap->ops->check_status (usually
ata_check_status)

libata-sff uses the wrong one. Hardly suprising given the naming here,
which ought to get fixed to ata_sff_check_status() perhaps ?

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