intrabc: replace prob with cdf

Improves keyframe coding by 0.1% on the screen_content testset.

Change-Id: I5793a67eaae21010ef200038af99ebb9029fc770
diff --git a/av1/encoder/rdopt.c b/av1/encoder/rdopt.c
index d31dd32..d6ef343 100644
--- a/av1/encoder/rdopt.c
+++ b/av1/encoder/rdopt.c
@@ -9648,7 +9648,6 @@
 
   MACROBLOCKD *const xd = &x->e_mbd;
   const TileInfo *tile = &xd->tile;
-  FRAME_CONTEXT *const ec_ctx = xd->tile_ctx;
   MODE_INFO *const mi = xd->mi[0];
   const int mi_row = -xd->mb_to_top_edge / (8 * MI_SIZE);
   const int mi_col = -xd->mb_to_left_edge / (8 * MI_SIZE);
@@ -9768,8 +9767,7 @@
     // in MV_COST_WEIGHT is too large. Explore other values.
     int rate_mv = av1_mv_bit_cost(&dv, &dv_ref.as_mv, x->nmvjointcost,
                                   x->mvcost, MV_COST_WEIGHT_SUB);
-    const int rate_mode = av1_cost_bit(ec_ctx->intrabc_prob, 1);
-
+    const int rate_mode = x->intrabc_cost[1];
     RD_STATS rd_stats, rd_stats_uv;
     av1_subtract_plane(x, bsize, 0);
     super_block_yrd(cpi, x, &rd_stats, bsize, INT64_MAX);