Small cleanup: reusing existing code.

Change-Id: Iac4775ad98e988f2b9cf5bd0dc91ab994d0262ce

vp9/encoder/vp9_pickmode.c

@@ -394,7 +394,7 @@ static void estimate_block_intra(int plane, int block, BLOCK_SIZE plane_bsize,
   args->dist += dist;
 }
 
-static const THR_MODES mode_idx[MAX_REF_FRAMES - 1][4] = {
+static const THR_MODES mode_idx[MAX_REF_FRAMES - 1][INTER_MODES] = {
   {THR_NEARESTMV, THR_NEARMV, THR_ZEROMV, THR_NEWMV},
   {THR_NEARESTG, THR_NEARG, THR_ZEROG, THR_NEWG},
   {THR_NEARESTA, THR_NEARA, THR_ZEROA, THR_NEWA},
@@ -547,7 +547,7 @@ int64_t vp9_pick_inter_mode(VP9_COMP *cpi, MACROBLOCK *x,
         continue;
 
       mode_rd_thresh =  rd_threshes[mode_idx[ref_frame - LAST_FRAME]
-                                            [this_mode - NEARESTMV]];
+                                    [INTER_OFFSET(this_mode)]];
       if (rd_less_than_thresh(best_rd, mode_rd_thresh,
                               rd_thresh_freq_fact[this_mode]))
         continue;