avfilter: make avfilter_graph_get_filter use const string name

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/avfilter.h

@@ -1272,7 +1272,7 @@ AVFilterContext *avfilter_graph_alloc_filter(AVFilterGraph *graph,
  * @return the pointer to the found filter instance or NULL if it
  * cannot be found.
  */
-AVFilterContext *avfilter_graph_get_filter(AVFilterGraph *graph, char *name);
+AVFilterContext *avfilter_graph_get_filter(AVFilterGraph *graph, const char *name);
 
 #if FF_API_AVFILTER_OPEN
 /**

libavfilter/avfiltergraph.c

@@ -281,7 +281,7 @@ static int graph_config_links(AVFilterGraph *graph, AVClass *log_ctx)
     return 0;
 }
 
-AVFilterContext *avfilter_graph_get_filter(AVFilterGraph *graph, char *name)
+AVFilterContext *avfilter_graph_get_filter(AVFilterGraph *graph, const char *name)
 {
     int i;