spi/s3c64xx: use correct dma_transfer_direction type

There is a subtle difference between dma_transfer_direction and
dma_data_direction: the former is used by the dmaengine framework,
while the latter is used by the dma-mapping API. Although the
purpose is comparable, the actual values are different and must
not be mixed. In this case, the driver just wants to use
dma_transfer_direction.

Without this patch, building s3c6400_defconfig results in:

drivers/spi/spi-s3c64xx.c: In function 's3c64xx_spi_dmacb':
drivers/spi/spi-s3c64xx.c:239:21: warning: comparison between
	'enum dma_data_direction' and 'enum dma_transfer_direction' [-Wenum-compare]

As pointed out by Kukjin Kim, this also changes the use of constants
from DMA_FROM_DEVICE/DMA_TO_DEVICE to DMA_DEV_TO_MEM/DMA_MEM_TO_DEV.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kukjin Kim <kgene.kim@samsung.com>
Cc: Ben Dooks <ben-linux@fluff.org>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-samsung-soc@vger.kernel.org
Cc: spi-devel-general@lists.sourceforge.net