ALSA: snd-usb-6fire: add analog input volume control

Add a stereo volume control for analog input channel pair 1/2.

Signed-off-by: Torsten Schenk <torsten.schenk@zoho.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/usb/6fire/control.h b/sound/usb/6fire/control.h
index 9f9eb64..9a596d9 100644
--- a/sound/usb/6fire/control.h
+++ b/sound/usb/6fire/control.h
@@ -46,6 +46,8 @@
 	u8 output_vol[6];
 	u8 ovol_updated;
 	u8 output_mute;
+	s8 input_vol[2];
+	u8 ivol_updated;
 };
 
 int __devinit usb6fire_control_init(struct sfire_chip *chip);