ALSA: hda - patch_analog.c: Remove some unused functions

Removes some functions that are not used anywhere:
ad198x_ch_mode_get() ad198x_ch_mode_info() ad198x_ch_mode_info()

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>