spi: spi-davinci: Fix direction in dma_map_single()

Commit 048177ce (spi: spi-davinci:
convert to DMA engine API) introduced a regression: dma_map_single()
is called with direction DMA_FROM_DEVICE for rx and for tx.
Signed-off-by: Christian Eggers <ceggers@gmx.de>
Acked-by: Matt Porter <mporter@ti.com>
Signed-off-by: Mark Brown <broonie@linaro.org>
Cc: stable@vger.kernel.org # v3.7.x+

drivers/spi/spi-davinci.c

@@ -609,7 +609,7 @@ static int davinci_spi_bufs(struct spi_device *spi, struct spi_transfer *t)
 		else
 			buf = (void *)t->tx_buf;
 		t->tx_dma = dma_map_single(&spi->dev, buf,
-				t->len, DMA_FROM_DEVICE);
+				t->len, DMA_TO_DEVICE);
 		if (!t->tx_dma) {
 			ret = -EFAULT;
 			goto err_tx_map;