ASoC: fsl_dma: Use managed buffer allocation

ASoC: fsl_dma: Use managed buffer allocation

This patch simplifies the buffer pre-allocation code of fsl_dma
driver with the standard managed buffer helper.  It uses the newly
introduced fixed-size buffer allocation helper.

Cc: Nicolin Chen <nicoleotsuka@gmail.com>
Cc: Xiubo Li <Xiubo.Lee@gmail.com>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Shengjiu Wang <shengjiu.wang@gmail.com>
Acked-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20210802072815.13551-12-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>