Update segment tree_cdf per frame.

Move computing the segmentation_probs.tree_cdf table per symbol to
 computing it only when the probabilities are updated.

Change-Id: I3826418094bbaca4ded87de5ff04d4b27c85e35a

av1/encoder/segmentation.c

@@ -366,6 +366,9 @@ void av1_choose_segmap_coding_method(AV1_COMMON *cm, MACROBLOCKD *xd) {
   } else {
     seg->temporal_update = 0;
   }
+#if CONFIG_DAALA_EC
+  av1_tree_to_cdf(av1_segment_tree, segp->tree_probs, segp->tree_cdf);
+#endif
 }
 
 void av1_reset_segment_features(AV1_COMMON *cm) {