ide: remove ->dma_{status,command} fields from ide_hwif_t

* Use ->dma_base + offset instead of ->dma_{status,command}
  and remove no longer needed ->dma_{status,command}.

While at it:

* Use ATA_DMA_* defines.

There should be no functional changes caused by this patch.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
diff --git a/drivers/ide/ide-iops.c b/drivers/ide/ide-iops.c
index a09bf43..17cad6c 100644
--- a/drivers/ide/ide-iops.c
+++ b/drivers/ide/ide-iops.c
@@ -106,9 +106,9 @@
 static u8 ide_read_sff_dma_status(ide_hwif_t *hwif)
 {
 	if (hwif->host_flags & IDE_HFLAG_MMIO)
-		return readb((void __iomem *)hwif->dma_status);
+		return readb((void __iomem *)(hwif->dma_base + ATA_DMA_STATUS));
 	else
-		return inb(hwif->dma_status);
+		return inb(hwif->dma_base + ATA_DMA_STATUS);
 }
 
 static void ide_tf_load(ide_drive_t *drive, ide_task_t *task)