c_dig_rx is no longer nullable (helps with timing due to issue with compiler checks)

module_usb_audio/audio.h

@@ -1,6 +1,7 @@
 #ifndef __audio_h__
 #define __audio_h__
 
+#include "devicedefines.h"
 /** The audio driver thread.
  *
  *  This function drives I2S ports and handles samples to/from other digital
@@ -13,6 +14,10 @@
  *  \param c_config An optional channel that will be passed on to the
  *                  CODEC configuration functions.
  */
-void audio(chanend c_in, chanend ?c_dig, chanend ?c_config, chanend ?c_adc);
+void audio(chanend c_in, 
+#if (defined(SPDIF_RX) || defined(ADAT_RX))    
+    chanend c_dig, 
+#endif
+    chanend ?c_config, chanend ?c_adc);
 
 #endif // __audio_h__