1) Create seperate mixer controls for each ADC
2) Make number of substreams of capture PCM device be equal to
   number of ADCs
Signed-off-by: NMaxim Levitsky <maximlevitsky@gmail.com>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>
Signed-off-by: NJaroslav Kysela <perex@suse.cz>