ALSA: ice1712: wm8766: Remove some unused functions

Removes some functions that are not used anywhere:
snd_wm8766_set_power() snd_wm8766_set_master_mode()

This was partially found by using a static code analysis program called cppcheck.

Signed-off-by: Rickard Strandqvist <rickard_strandqvist@spectrumdigital.se>
Signed-off-by: Takashi Iwai <tiwai@suse.de>