Fix -Wformat-security related

Author: rouault

src/wfs/wfs_get_feature.c

@@ -795,7 +795,7 @@ static void wfs_geojson_display_results(ows * o, wfs_request * wr, mlist * reque
          assert(wr->callback);
 
          fprintf(o->output, "Content-Type: application/javascript\n\n");
-         fprintf(o->output, wr->callback->buf);
+         fprintf(o->output, "%s", wr->callback->buf);
          fprintf(o->output, "(");
 
   } else fprintf(o->output, "Content-Type: application/json\n\n");