fftools/ffmpeg_filter: make configure_filtergraph() static

It is no longer used outside of ffmpeg_filter.

fftools/ffmpeg.h

@@ -726,7 +726,6 @@ const AVCodec *find_codec_or_die(void *logctx, const char *name,
                                  enum AVMediaType type, int encoder);
 int parse_and_set_vsync(const char *arg, int *vsync_var, int file_idx, int st_idx, int is_global);
 
-int configure_filtergraph(FilterGraph *fg);
 void check_filter_outputs(void);
 int filtergraph_is_simple(const FilterGraph *fg);
 int init_simple_filtergraph(InputStream *ist, OutputStream *ost,

fftools/ffmpeg_filter.c

@@ -133,6 +133,8 @@ static InputFilterPriv *ifp_from_ifilter(InputFilter *ifilter)
     return (InputFilterPriv*)ifilter;
 }
 
+static int configure_filtergraph(FilterGraph *fg);
+
 static int sub2video_get_blank_frame(InputFilterPriv *ifp)
 {
     AVFrame *frame = ifp->sub2video.frame;
@@ -1496,7 +1498,7 @@ static int graph_is_meta(AVFilterGraph *graph)
     return 1;
 }
 
-int configure_filtergraph(FilterGraph *fg)
+static int configure_filtergraph(FilterGraph *fg)
 {
     FilterGraphPriv *fgp = fgp_from_fg(fg);
     AVBufferRef *hw_device;