av1_predict_intra_block_facade: const correctness.

BUG=aomedia:448

Change-Id: Idc76c954435517a50a9cfa8e54fb73a593aaaac6
diff --git a/av1/common/reconintra.c b/av1/common/reconintra.c
index 7a33650..5477d6d 100644
--- a/av1/common/reconintra.c
+++ b/av1/common/reconintra.c
@@ -2291,9 +2291,10 @@
   const int dst_stride = pd->dst.stride;
   uint8_t *dst =
       &pd->dst.buf[(blk_row * dst_stride + blk_col) << tx_size_wide_log2[0]];
-  MB_MODE_INFO *mbmi = &xd->mi[0]->mbmi;
-  int block_raster_idx = av1_block_index_to_raster_order(tx_size, block_idx);
-  PREDICTION_MODE mode =
+  const MB_MODE_INFO *const mbmi = &xd->mi[0]->mbmi;
+  const int block_raster_idx =
+      av1_block_index_to_raster_order(tx_size, block_idx);
+  const PREDICTION_MODE mode =
       (plane == 0) ? get_y_mode(xd->mi[0], block_raster_idx) : mbmi->uv_mode;
   av1_predict_intra_block(xd, pd->width, pd->height, txsize_to_bsize[tx_size],
                           mode, dst, dst_stride, dst, dst_stride, blk_col,