ide: move ide_map_sg() call out of ->dma_setup method (take 2)

Move ide_map_sg() call from ->dma_setup implementations and
ide_destroy_dmatable() one from *_build_dmatable() to ide_dma_prepare().

There should be no functional changes caused by this patch.

Sergei:
Removed 'use_pio_instead' labels and replaced 'goto' with 'return 0' --
that required no changes to the follow-up patches...

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
diff --git a/drivers/ide/tx4939ide.c b/drivers/ide/tx4939ide.c
index f62ced8..7267c46 100644
--- a/drivers/ide/tx4939ide.c
+++ b/drivers/ide/tx4939ide.c
@@ -279,8 +279,6 @@
 	printk(KERN_ERR "%s: %s\n", drive->name,
 		count ? "DMA table too small" : "empty DMA table?");
 
-	ide_destroy_dmatable(drive);
-
 	return 0; /* revert to PIO for this request */
 }
 #else
@@ -294,10 +292,8 @@
 	u8 rw = (cmd->tf_flags & IDE_TFLAG_WRITE) ? 0 : ATA_DMA_WR;
 
 	/* fall back to PIO! */
-	if (tx4939ide_build_dmatable(drive, cmd) == 0) {
-		ide_map_sg(drive, cmd);
+	if (tx4939ide_build_dmatable(drive, cmd) == 0)
 		return 1;
-	}
 
 	/* PRD table */
 	tx4939ide_writel(hwif->dmatable_dma, base, TX4939IDE_PRD_Ptr);