spi: dw-mid: split rx and tx callbacks when DMA

Currently driver wouldn't work properly if user asked for simplex transfer. The
patch separates DMA rx and tx callbacks and finishes transfer correctly in any
case.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
diff --git a/drivers/spi/spi-dw.h b/drivers/spi/spi-dw.h
index 83a103a..3d32be6 100644
--- a/drivers/spi/spi-dw.h
+++ b/drivers/spi/spi-dw.h
@@ -139,7 +139,7 @@
 	struct scatterlist	tx_sgl;
 	struct dma_chan		*rxchan;
 	struct scatterlist	rx_sgl;
-	int			dma_chan_done;
+	unsigned long		dma_chan_busy;
 	struct device		*dma_dev;
 	dma_addr_t		dma_addr; /* phy address of the Data register */
 	struct dw_spi_dma_ops	*dma_ops;