ASoC: odrodix2_max98090: Make non exported symbols static

ASoC: odrodix2_max98090: Make non exported symbols static

odroidx2_drvdata and odroidu3_drvdata are not used outside this module so make
them static (and also const while we are at it).

Fixes the following warnings from sparse:
    sound/soc/samsung/odroidx2_max98090.c:69:26: warning: symbol
     'odroidx2_drvdata' was not declared. Should it be static?
    sound/soc/samsung/odroidx2_max98090.c:74:26: warning: symbol
     'odroidu3_drvdata' was not declared. Should it be static?

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@linaro.org>