avcodec/mpeg_er: Don't set block_index unnecessarily

ff_init_block_index() sets MpegEncContext.dest and
MpegEncContext.block_index. The latter is unused by
ff_mpv_reconstruct_mb() (which is what this code is
preparatory for) and dest is overwritten a few lines below.
So don't initialize block_index at all.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/mpeg_er.c

@@ -76,10 +76,6 @@ static void mpeg_er_decode_mb(void *opaque, int ref, int mv_dir, int mv_type,
     s->mcsel      = 0;
     memcpy(s->mv, mv, sizeof(*mv));
 
-    ff_init_block_index(s);
-    ff_update_block_index(s, s->avctx->bits_per_raw_sample,
-                          s->avctx->lowres, s->chroma_x_shift);
-
     s->bdsp.clear_blocks(s->block[0]);
     if (!s->chroma_y_shift)
         s->bdsp.clear_blocks(s->block[6]);