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_vsc.c b/drivers/ata/sata_vsc.c
index 2c3c769..f3d635c 100644
--- a/drivers/ata/sata_vsc.c
+++ b/drivers/ata/sata_vsc.c
@@ -251,7 +251,7 @@
 	 * simply clear the interrupt
 	 */
 	if (unlikely(!handled))
-		ap->ops->check_status(ap);
+		ap->ops->sff_check_status(ap);
 }
 
 /*
@@ -306,8 +306,8 @@
 
 static struct ata_port_operations vsc_sata_ops = {
 	.inherits		= &ata_bmdma_port_ops,
-	.tf_load		= vsc_sata_tf_load,
-	.tf_read		= vsc_sata_tf_read,
+	.sff_tf_load		= vsc_sata_tf_load,
+	.sff_tf_read		= vsc_sata_tf_read,
 	.freeze			= vsc_freeze,
 	.thaw			= vsc_thaw,
 	.scr_read		= vsc_sata_scr_read,