[libata] Use ATA_UDMAx standard masks when filling driver's udma_mask info

The ATA_UDMAx masks are self-documenting, and far better than manually
writing in the hex mask.

Note that pata_it8213 mask differed from the comment.  Added a FIXME there.

Signed-off-by: Jeff Garzik <jeff@garzik.org>
diff --git a/drivers/ata/sata_sis.c b/drivers/ata/sata_sis.c
index f111c98..fd80bcf 100644
--- a/drivers/ata/sata_sis.c
+++ b/drivers/ata/sata_sis.c
@@ -133,7 +133,7 @@
 	.flags		= ATA_FLAG_SATA | ATA_FLAG_NO_LEGACY,
 	.pio_mask	= 0x1f,
 	.mwdma_mask	= 0x7,
-	.udma_mask	= 0x7f,
+	.udma_mask	= ATA_UDMA6,
 	.port_ops	= &sis_ops,
 };