libavfilter/dnn_interface.c: fix av_freep dnn_module.

Signed-off-by: Pedro Arthur <bygrandao@gmail.com>

libavfilter/dnn_interface.c

@@ -51,7 +51,7 @@ DNNModule* ff_get_dnn_module(DNNBackendType backend_type)
         dnn_module->execute_model = &ff_dnn_execute_model_tf;
         dnn_module->free_model = &ff_dnn_free_model_tf;
     #else
-        av_freep(dnn_module);
+        av_freep(&dnn_module);
         return NULL;
     #endif
     }