ALSA: usb-audio: don't hardcode gain for output channel of Presonus Studio

On the 1824c output channel 4 left/right is the S/PDIF output,
so this needs to be able to be set.

I'm guessing that for the 1810c since it has no output channel 4,
it does not matter what the gain value of this channel is set to.

Signed-off-by: Roy Vegard Ovesen <roy.vegard.ovesen@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

Author: royvegard

sound/usb/mixer_s1810c.c

@@ -147,12 +147,7 @@ snd_s1810c_send_ctl_packet(struct usb_device *dev, u32 a,
 	pkt.b = b;
 	pkt.c = c;
 	pkt.d = d;
-	/*
-	 * Value for settings 0/1 for this
-	 * output channel is always 0 (probably because
-	 * there is no ADAT output on 1810c)
-	 */
-	pkt.e = (c == 4) ? 0 : e;
+	pkt.e = e;
 
 	ret = snd_usb_ctl_msg(dev, usb_sndctrlpipe(dev, 0),
 			      SC1810C_CMD_REQ,