ASoC: wm8580: Fix non static symbol warnings

Fixes the following sparse warnings:

sound/soc/codecs/wm8580.c:988:33: warning:
 symbol 'wm8580_data' was not declared. Should it be static?
sound/soc/codecs/wm8580.c:992:33: warning:
 symbol 'wm8581_data' was not declared. Should it be static?

Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Mark Brown <broonie@kernel.org>