ASoC: cygnus: Remove unused declarations

Commit a6ee05d94e8f ("ASoC: cygnus: Add Cygnus audio DAI driver")
declared but never implemented these.

Signed-off-by: Yue Haibing <[e-mail]
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Mark Brown <[e-mail]

sound/soc/bcm/cygnus-ssp.h

···
 	unsigned long vco_rate;
 };
 
-extern int cygnus_ssp_get_mode(struct snd_soc_dai *cpu_dai);
-extern int cygnus_ssp_add_pll_tweak_controls(struct snd_soc_pcm_runtime *rtd);
 extern int cygnus_ssp_set_custom_fsync_width(struct snd_soc_dai *cpu_dai,
 						int len);
 extern int cygnus_soc_platform_register(struct device *dev,