ASoC: codec: fix the sparse check warnings.

Some thing Likes:

reproduce: make C=1 CF=-D__CHECK_ENDIAN__

sparse warnings: (new ones prefixed by >>)

>> sound/soc/codecs/wm8997.c:1084:15: sparse: symbol \
'wm8997_get_regmap' was not declared. Should it be static?

Signed-off-by: Xiubo Li <Li.Xiubo@freescale.com>
Signed-off-by: Mark Brown <broonie@linaro.org>