sound: virtuoso: add Xonar DS support

Add experimental support for the Asus Xonar DS.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>
diff --git a/sound/pci/oxygen/xonar.h b/sound/pci/oxygen/xonar.h
index 89b3ed8..b35343b 100644
--- a/sound/pci/oxygen/xonar.h
+++ b/sound/pci/oxygen/xonar.h
@@ -35,6 +35,8 @@
 			    const struct pci_device_id *id);
 int get_xonar_cs43xx_model(struct oxygen *chip,
 			   const struct pci_device_id *id);
+int get_xonar_wm87x6_model(struct oxygen *chip,
+			   const struct pci_device_id *id);
 
 /* HDMI helper functions */