[libata] Clean up driver udma_mask initializers

* Use ATA_UDMA*
* Remove FIXME notations that once served to remind us to verify
  that these were indeed the correct UDMA masks.  They are.

Signed-off-by: Jeff Garzik <jeff@garzik.org>
diff --git a/drivers/ata/sata_sx4.c b/drivers/ata/sata_sx4.c
index 3d83ee2..5193bd8 100644
--- a/drivers/ata/sata_sx4.c
+++ b/drivers/ata/sata_sx4.c
@@ -279,7 +279,7 @@
 				  ATA_FLAG_NO_ATAPI | ATA_FLAG_PIO_POLLING,
 		.pio_mask	= 0x1f, /* pio0-4 */
 		.mwdma_mask	= 0x07, /* mwdma0-2 */
-		.udma_mask	= 0x7f, /* udma0-6 ; FIXME */
+		.udma_mask	= ATA_UDMA6,
 		.port_ops	= &pdc_20621_ops,
 	},