Using TREE_SIZE macro for vp9_segment_tree.

Change-Id: I2965453135643d8f061b9fa9406fdca2db9c961e

vp9/common/vp9_seg_common.c

@@ -76,7 +76,7 @@ int vp9_get_segdata(const struct segmentation *seg, int segment_id,
 }
 
 
-const vp9_tree_index vp9_segment_tree[14] = {
+const vp9_tree_index vp9_segment_tree[TREE_SIZE(MAX_SEGMENTS)] = {
   2,  4,  6,  8, 10, 12,
   0, -1, -2, -3, -4, -5, -6, -7
 };

vp9/common/vp9_seg_common.h

@@ -76,7 +76,7 @@ int vp9_get_segdata(const struct segmentation *seg,
                     int segment_id,
                     SEG_LVL_FEATURES feature_id);
 
-extern const vp9_tree_index vp9_segment_tree[14];
+extern const vp9_tree_index vp9_segment_tree[TREE_SIZE(MAX_SEGMENTS)];
 
 #endif  // VP9_COMMON_VP9_SEG_COMMON_H_