libata: add @is_cmd to ata_tf_to_fis()

Add @is_cmd to ata_tf_to_fis().  This controls bit 7 of the second
byte which tells the device whether this H2D FIS is for a command or
not.  This cleans up ahci a bit and will be used by PMP.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
diff --git a/drivers/ata/sata_qstor.c b/drivers/ata/sata_qstor.c
index 9ab554d..5aef4ac 100644
--- a/drivers/ata/sata_qstor.c
+++ b/drivers/ata/sata_qstor.c
@@ -337,7 +337,7 @@
 	buf[28] = dflags;
 
 	/* frame information structure (FIS) */
-	ata_tf_to_fis(&qc->tf, &buf[32], 0);
+	ata_tf_to_fis(&qc->tf, 0, 1, &buf[32]);
 }
 
 static inline void qs_packet_start(struct ata_queued_cmd *qc)