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_sil.c b/drivers/ata/sata_sil.c
index 987313b..88bf421 100644
--- a/drivers/ata/sata_sil.c
+++ b/drivers/ata/sata_sil.c
@@ -369,7 +369,7 @@
 
 	if (unlikely(!qc || (qc->tf.flags & ATA_TFLAG_POLLING))) {
 		/* this sometimes happens, just clear IRQ */
-		ap->ops->check_status(ap);
+		ap->ops->sff_check_status(ap);
 		return;
 	}
 
@@ -405,7 +405,7 @@
 	}
 
 	/* check main status, clearing INTRQ */
-	status = ap->ops->check_status(ap);
+	status = ap->ops->sff_check_status(ap);
 	if (unlikely(status & ATA_BUSY))
 		goto err_hsm;
 
@@ -480,7 +480,7 @@
 	u32 tmp;
 
 	/* clear IRQ */
-	ap->ops->check_status(ap);
+	ap->ops->sff_check_status(ap);
 	ata_sff_irq_clear(ap);
 
 	/* turn on SATA IRQ if supported */