ASoC: cygnus: Remove unused declarations

Commit a6ee05d9 ("ASoC: cygnus: Add Cygnus audio DAI driver")
declared but never implemented these.

Signed-off-by: Yue Haibing <yuehaibing@huawei.com>
Link: https://lore.kernel.org/r/20230811110021.31656-1-yuehaibing@huawei.com


Signed-off-by: Mark Brown <broonie@kernel.org>