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>