lavfi: make two functions static.

ff_request_frame_to_filter() and ff_filter_frame_to_filter()
are only used in avfilter.c.

libavfilter/avfilter.c

@@ -429,7 +429,7 @@ int ff_request_frame(AVFilterLink *link)
     return 0;
 }
 
-int ff_request_frame_to_filter(AVFilterLink *link)
+static int ff_request_frame_to_filter(AVFilterLink *link)
 {
     int ret = -1;
 
@@ -1249,7 +1249,7 @@ static int take_samples(AVFilterLink *link, unsigned min, unsigned max,
     return 0;
 }
 
-int ff_filter_frame_to_filter(AVFilterLink *link)
+static int ff_filter_frame_to_filter(AVFilterLink *link)
 {
     AVFrame *frame = NULL;
     AVFilterContext *dst = link->dst;

libavfilter/internal.h

@@ -339,10 +339,6 @@ int ff_poll_frame(AVFilterLink *link);
  */
 int ff_request_frame(AVFilterLink *link);
 
-int ff_request_frame_to_filter(AVFilterLink *link);
-
-int ff_filter_frame_to_filter(AVFilterLink *link);
-
 #define AVFILTER_DEFINE_CLASS(fname)            \
     static const AVClass fname##_class = {      \
         .class_name = #fname,                   \