ASoC: fix trivial build error in mpc5200_dma.c

Add the obvious header to fix this:

sound/soc/fsl/mpc5200_dma.c:301: error: implicit declaration of function 'DMA_BIT_MASK'
sound/soc/fsl/mpc5200_dma.c:301: error: initializer element is not constant
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

sound/soc/fsl/mpc5200_dma.c

@@ -8,6 +8,7 @@
 
 #include <linux/module.h>
 #include <linux/of_device.h>
+#include <linux/dma-mapping.h>
 #include <linux/slab.h>
 #include <linux/of_platform.h>