libata: rename SFF port ops

Add sff_ prefix to SFF specific port ops.

This rename is in preparation of separating SFF support out of libata
core layer.  This patch strictly renames ops and doesn't introduce any
behavior difference.

Signed-off-by: Tejun Heo <htejun@gmail.com>
diff --git a/drivers/ata/sata_via.c b/drivers/ata/sata_via.c
index 9323bc2..e5df376 100644
--- a/drivers/ata/sata_via.c
+++ b/drivers/ata/sata_via.c
@@ -173,7 +173,7 @@
 	/* Some VIA controllers choke if ATA_NIEN is manipulated in
 	 * certain way.  Leave it alone and just clear pending IRQ.
 	 */
-	ap->ops->check_status(ap);
+	ap->ops->sff_check_status(ap);
 	ata_sff_irq_clear(ap);
 }