ASoC: AMD: remove unused ‘dma_buffer’

In acp_dma_hw_params(), 'dma_buffer' is initialized, but not used. So
remove it.

sound/soc/amd/acp-pcm-dma.c: In function ‘acp_dma_hw_params’:
sound/soc/amd/acp-pcm-dma.c:673:25: warning: variable ‘dma_buffer’ set but not used [-Wunused-but-set-variable]
  struct snd_dma_buffer *dma_buffer;

Cc: Maruthi Bayyavarapu <maruthi.bayyavarapu@amd.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>