audio_mp3: Report file position and duration

The media framework allows the position and duration to use
unspecified units, so do just that. It's better than nothing
and it's already used by mp3_draw anyway.

components/audio_mp3/audio_mp3.c

@@ -152,6 +152,12 @@ static void mp3_think(st3m_media *media, float ms_elapsed) {
 
     if (self->control.paused) return;
 
+    if (self->file) {
+        self->control.position = self->offset;
+        if (self->offset + 512 >= self->file_size)
+            self->control.position = self->file_size;
+    }
+
     if (!self->started) {
         self->started = 1;
         mp3_think(media, 100);
@@ -373,6 +379,6 @@ st3m_media *st3m_media_load_mp3(const char *path) {
         return NULL;
     }
     mp3dec_init(&self->mp3d);
-    self->control.duration = -1;
+    self->control.duration = self->file_size;
     return (st3m_media *)self;
 }