Fix filter intra backward prob update

Resolve the enc/dec mismatch issue when filter intra is turned on,
in addition to chroma-sub8x8, ext-tx, and ext-inter experiments.

BUG=aomedia:570

Change-Id: Idf0875763ce24bd8d4022f7338fc86debf4dfd0c

av1/encoder/encodeframe.c

@@ -5199,6 +5199,11 @@ static void sum_intra_stats(FRAME_COUNTS *counts, MACROBLOCKD *xd,
       ++counts->filter_intra[0][use_filter_intra_mode];
     }
     if (mbmi->uv_mode == DC_PRED
+#if CONFIG_CB4X4
+        &&
+        is_chroma_reference(mi_row, mi_col, bsize, xd->plane[1].subsampling_x,
+                            xd->plane[1].subsampling_y)
+#endif
 #if CONFIG_PALETTE
         && mbmi->palette_mode_info.palette_size[1] == 0
 #endif  // CONFIG_PALETTE