ASoC: edma-pcm: Include edma-pcm.h

edma_pcm_platform_register() is declared in edma-pcm.h and defined in
edma-pcm.c. To make sure that the function signature matches for both
edma-pcm.c should include edma-pcm.h

Fixes the following sparse warning:
	sound/soc/davinci/edma-pcm.c:48:5: warning: symbol
	 'edma_pcm_platform_register' was not declared. Should it be static?

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@linaro.org>