Fix encoder failure in segmentation mode

This commit fixes an encoder segment fault in the codebase, when
the segmentation feature is turned on. The issue was introduced in

5cce322 Porting ext_partition experiment from nextgen

Change-Id: Ifb4c06c5a6976114a8bd061d40d0338a136abaaf

vp10/encoder/segmentation.c

@@ -168,14 +168,12 @@ static void count_segs_sb(const VP10_COMMON *cm, MACROBLOCKD *xd,
 #if CONFIG_EXT_PARTITION_TYPES
   PARTITION_TYPE partition;
 #else
-  const int bw = num_8x8_blocks_wide_lookup[mi[0]->mbmi.sb_type];
-  const int bh = num_8x8_blocks_high_lookup[mi[0]->mbmi.sb_type];
+  int bw, bh;
 #endif  // CONFIG_EXT_PARTITION_TYPES
 
   if (mi_row >= cm->mi_rows || mi_col >= cm->mi_cols)
     return;
 
-
 #if CONFIG_EXT_PARTITION_TYPES
   if (bsize == BLOCK_8X8)
     partition = PARTITION_NONE;
@@ -263,6 +261,9 @@ static void count_segs_sb(const VP10_COMMON *cm, MACROBLOCKD *xd,
       assert(0);
   }
 #else
+  bw = num_8x8_blocks_wide_lookup[mi[0]->mbmi.sb_type];
+  bh = num_8x8_blocks_high_lookup[mi[0]->mbmi.sb_type];
+
   if (bw == bs && bh == bs) {
     count_segs(cm, xd, tile, mi, no_pred_segcounts, temporal_predictor_count,
                t_unpred_seg_counts, bs, bs, mi_row, mi_col);