ASoC: rt5663: fix sparse warnings

Fixes the following sparse warnings:

sound/soc/codecs/rt5663.c:1367:14: warning: duplicate const
sound/soc/codecs/rt5663.c:1577:5: warning:
 symbol 'rt5663_button_detect' was not declared. Should it be static?
sound/soc/codecs/rt5663.c:2857:24: warning:
 symbol 'rt5663_aif_dai_ops' was not declared. Should it be static?
sound/soc/codecs/rt5663.c:2866:27: warning:
 symbol 'rt5663_dai' was not declared. Should it be static?
sound/soc/codecs/rt5663.c:3193:6: warning:
 symbol 'rt5663_i2c_shutdown' was not declared. Should it be static?
sound/soc/codecs/rt5663.c:3200:19: warning:
 symbol 'rt5663_i2c_driver' was not declared. Should it be static?

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