dnn_interface.h: fix redefining typedefs

Signed-off-by: Guo, Yejun <yejun.guo@intel.com>

libavfilter/dnn_interface.h

@@ -28,7 +28,7 @@
 
 #include <stdint.h>
 #include "libavutil/frame.h"
-typedef struct AVFilterContext AVFilterContext;
+#include "avfilter.h"
 
 typedef enum {DNN_SUCCESS, DNN_ERROR} DNNReturnType;