USB: Move vendor subclass definition from usb/audio.h to usb/ch9.h

USB_SUBCLASS_VENDOR_SPEC is common to several USB classes and as such belongs
to usb/ch9.h.

Signed-off-by: Laurent Pinchart <laurent.pinchart@skynet.be>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
diff --git a/include/linux/usb/ch9.h b/include/linux/usb/ch9.h
index 8f8b741..94012e6 100644
--- a/include/linux/usb/ch9.h
+++ b/include/linux/usb/ch9.h
@@ -258,6 +258,8 @@
 #define USB_CLASS_APP_SPEC		0xfe
 #define USB_CLASS_VENDOR_SPEC		0xff
 
+#define USB_SUBCLASS_VENDOR_SPEC	0xff
+
 /*-------------------------------------------------------------------------*/
 
 /* USB_DT_CONFIG: Configuration descriptor information.