Fix compile warnings with inspector

Change-Id: I055c0f23f4edf71cb01b72e573f0949e53f72dd1
diff --git a/av1/decoder/inspection.h b/av1/decoder/inspection.h
index c2ffe90..67ddad7 100644
--- a/av1/decoder/inspection.h
+++ b/av1/decoder/inspection.h
@@ -20,7 +20,9 @@
 #include "av1/decoder/accounting.h"
 #endif
 
+#ifndef AOM_AOMDX_H_
 typedef void (*aom_inspect_cb)(void *decoder, void *data);
+#endif
 
 typedef struct insp_mv insp_mv;