spi: dw-mid: change magic numbers to the constants

Instead of using magic numbers in the code we create a bit map definition of
the DMACR register and use it.

There is no functional change.

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-mid.c b/drivers/spi/spi-dw-mid.c
index ecae30f..7bdf937 100644
--- a/drivers/spi/spi-dw-mid.c
+++ b/drivers/spi/spi-dw-mid.c
@@ -124,9 +124,9 @@
 		dw_writew(dws, DW_SPI_DMARDLR, 0xf);
 		dw_writew(dws, DW_SPI_DMATDLR, 0x10);
 		if (dws->tx_dma)
-			dma_ctrl |= 0x2;
+			dma_ctrl |= SPI_DMA_TDMAE;
 		if (dws->rx_dma)
-			dma_ctrl |= 0x1;
+			dma_ctrl |= SPI_DMA_RDMAE;
 		dw_writew(dws, DW_SPI_DMACR, dma_ctrl);
 		spi_enable_chip(dws, 1);
 	}