[ALSA] ice1724 - Add PCM Playback Switch to Revo 7.1

This patch adds the support of mute for front channels of M-Audio
Revolution 7.1 (the DAC AK4381 features a mute bit).

Signed-off-by: Pavel Hofman <dustin@seznam.cz>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>

sound/pci/ice1712/revo.c

@@ -186,7 +186,12 @@ static int revo51_i2c_init(struct snd_ice1712 *ice,
 #define AK_DAC(xname,xch) { .name = xname, .num_channels = xch }
 
 static const struct snd_akm4xxx_dac_channel revo71_front[] = {
-	AK_DAC("PCM Playback Volume", 2)
+	{
+		.name = "PCM Playback Volume",
+		.num_channels = 2,
+		/* front channels DAC supports muting */
+		.switch_name = "PCM Playback Switch",
+	},
 };
 
 static const struct snd_akm4xxx_dac_channel revo71_surround[] = {