snd_usb_clock_find_source
clock = snd_usb_clock_find_source(chip, fmt, true);
clock = snd_usb_clock_find_source(chip, fmt, false);
int snd_usb_clock_find_source(struct snd_usb_audio *chip,
int clock = snd_usb_clock_find_source(chip, fp, false);