libata-sff: prd is BMDMA specific

struct ata_prd and ap->prd are BMDMA specific.  Add bmdma_ prefix to
them and move them inside CONFIG_ATA_SFF.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
diff --git a/drivers/ata/sata_svw.c b/drivers/ata/sata_svw.c
index 7257f2d..101fd6a 100644
--- a/drivers/ata/sata_svw.c
+++ b/drivers/ata/sata_svw.c
@@ -224,7 +224,7 @@
 
 	/* load PRD table addr. */
 	mb();	/* make sure PRD table writes are visible to controller */
-	writel(ap->prd_dma, mmio + ATA_DMA_TABLE_OFS);
+	writel(ap->bmdma_prd_dma, mmio + ATA_DMA_TABLE_OFS);
 
 	/* specify data direction, triple-check start bit is clear */
 	dmactl = readb(mmio + ATA_DMA_CMD);