ALSA: snd-usb-6fire: Select missing SND_VMASTER option in Kconfig

Signed-off-by: NTorsten Schenk <torsten.schenk@zoho.com>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>

sound/usb/Kconfig

@@ -106,6 +106,7 @@ config SND_USB_6FIRE
         select BITREVERSE
         select SND_RAWMIDI
         select SND_PCM
+        select SND_VMASTER
         help
           Say Y here to include support for TerraTec 6fire DMX USB interface.