get_ref_frame: fix test for valid buffer.

In the current implementation of the encoder,
frame buffers may come from the wider set of
12 such buffers, and is not restricted to the
8 allowed as reference frames. This is only
an implementation detail and does not affect
the constraint of having a total of 8 reference
buffers overall.

Change-Id: I075f777146c2df49c275d89232933f8127235175

vp9/common/vp9_onyxc_int.h

@@ -207,7 +207,7 @@ static INLINE YV12_BUFFER_CONFIG *get_ref_frame(VP9_COMMON *cm, int index) {
     return NULL;
   if (cm->ref_frame_map[index] < 0)
     return NULL;
-  assert(cm->ref_frame_map[index] < REF_FRAMES);
+  assert(cm->ref_frame_map[index] < FRAME_BUFFERS);
   return &cm->frame_bufs[cm->ref_frame_map[index]].buf;
 }