Fixes the following sparse warning:

sound/soc/amd/acp-da7219-max98357a.c:46:12: warning:
 symbol 'da7219_dai_clk' was not declared. Should it be static?
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Mark Brown <broonie@kernel.org>