ALSA: usb-audio: make set_*_mix_values functions public

Make the functions set_cur_mix_value and get_cur_mix_value accessible by files
that include mixer.h. In addition make usb_mixer_elem_free accessible.
This allows reuse of these functions by mixers that may require quirks.

The following summarizes the renamed functions:
  - set_cur_mix_value -> snd_usb_set_cur_mix_value
  - get_cur_mix_value -> snd_usb_get_cur_mix_value
  - usb_mixer_elem_free -> snd_usb_mixer_elem_free

Signed-off-by: Chris J Arges <chris.j.arges@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/mixer.h

@@ -76,4 +76,12 @@ int snd_usb_mixer_suspend(struct usb_mixer_interface *mixer);
 int snd_usb_mixer_resume(struct usb_mixer_interface *mixer, bool reset_resume);
 #endif
 
+int snd_usb_set_cur_mix_value(struct usb_mixer_elem_info *cval, int channel,
+                             int index, int value);
+
+int snd_usb_get_cur_mix_value(struct usb_mixer_elem_info *cval,
+                             int channel, int index, int *value);
+
+extern void snd_usb_mixer_elem_free(struct snd_kcontrol *kctl);
+
 #endif /* __USBMIXER_H */