ASoC: sprd: Use managed buffer allocation

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

Acked-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20210802072815.13551-16-tiwai@suse.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>