nut: Use correct function pointer casts instead of void*

Fixes several warnings of the type
libavformat/nut.c:207:42: warning: ISO C forbids conversion of function pointer to object pointer type [-Wpedantic]

libavformat/nut.c

@@ -204,7 +204,8 @@ int ff_nut_add_sp(NUTContext *nut, int64_t pos, int64_t back_ptr, int64_t ts)
     sp->pos      = pos;
     sp->back_ptr = back_ptr;
     sp->ts       = ts;
-    av_tree_insert(&nut->syncpoints, sp, (void *) ff_nut_sp_pos_cmp, &node);
+    av_tree_insert(&nut->syncpoints, sp,
+                   (int (*)(void *, const void *)) ff_nut_sp_pos_cmp, &node);
     if (node) {
         av_free(sp);
         av_free(node);

libavformat/nutdec.c

@@ -987,7 +987,8 @@ static int read_seek(AVFormatContext *s, int stream_index,
         pos2 = st->index_entries[index].pos;
         ts   = st->index_entries[index].timestamp;
     } else {
-        av_tree_find(nut->syncpoints, &dummy, (void *) ff_nut_sp_pts_cmp,
+        av_tree_find(nut->syncpoints, &dummy,
+                     (int (*)(void *, const void *)) ff_nut_sp_pts_cmp,
                      (void **) next_node);
         av_log(s, AV_LOG_DEBUG, "%"PRIu64"-%"PRIu64" %"PRId64"-%"PRId64"\n",
                next_node[0]->pos, next_node[1]->pos, next_node[0]->ts,
@@ -1000,7 +1001,8 @@ static int read_seek(AVFormatContext *s, int stream_index,
         if (!(flags & AVSEEK_FLAG_BACKWARD)) {
             dummy.pos    = pos + 16;
             next_node[1] = &nopts_sp;
-            av_tree_find(nut->syncpoints, &dummy, (void *) ff_nut_sp_pos_cmp,
+            av_tree_find(nut->syncpoints, &dummy,
+                         (int (*)(void *, const void *)) ff_nut_sp_pos_cmp,
                          (void **) next_node);
             pos2 = ff_gen_search(s, -2, dummy.pos, next_node[0]->pos,
                                  next_node[1]->pos, next_node[1]->pos,
@@ -1011,7 +1013,8 @@ static int read_seek(AVFormatContext *s, int stream_index,
             // FIXME dir but I think it does not matter
         }
         dummy.pos = pos;
-        sp = av_tree_find(nut->syncpoints, &dummy, (void *) ff_nut_sp_pos_cmp,
+        sp = av_tree_find(nut->syncpoints, &dummy,
+                          (int (*)(void *, const void *)) ff_nut_sp_pos_cmp,
                           NULL);
 
         assert(sp);

libavformat/nutenc.c

@@ -807,7 +807,8 @@ static int nut_write_packet(AVFormatContext *s, AVPacket *pkt)
         }
         if (dummy.pos == INT64_MAX)
             dummy.pos = 0;
-        sp = av_tree_find(nut->syncpoints, &dummy, (void *)ff_nut_sp_pos_cmp,
+        sp = av_tree_find(nut->syncpoints, &dummy,
+                          (int (*)(void *, const void *)) ff_nut_sp_pos_cmp,
                           NULL);
 
         nut->last_syncpoint_pos = avio_tell(bc);