sound/soc/davinci/davinci-pcm.c: use gen_pool_dma_alloc() in davinci-pcm.c

Since gen_pool_dma_alloc() is introduced, we implement it to simplify code.

Signed-off-by: Nicolin Chen <b42378@freescale.com>
Cc: Liam Girdwood <lgirdwood@gmail.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Jaroslav Kysela <perex@perex.cz>
Cc: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>