Use INTER_OFFSET in vp9_pick_inter_mode

Cosmetic change to use pre-defined macros.

Change-Id: I93e9fa90113d0242599048940b39694660385a6f

vp9/common/vp9_blockd.h

@@ -89,7 +89,6 @@ static INLINE int is_inter_mode(MB_PREDICTION_MODE mode) {
 
 #define INTER_OFFSET(mode) ((mode) - NEARESTMV)
 
-
 /* For keyframes, intra block modes are predicted by the (already decoded)
    modes for the Y blocks to the left and above us; for interframes, there
    is a single probability table. */

vp9/encoder/vp9_pickmode.c

@@ -199,7 +199,7 @@ int64_t vp9_pick_inter_mode(VP9_COMP *cpi, MACROBLOCK *x,
     clamp_mv2(&frame_mv[NEARMV][ref_frame].as_mv, xd);
 
     for (this_mode = NEARESTMV; this_mode <= NEWMV; ++this_mode) {
-      int rate = cost[this_mode - NEARESTMV];
+      int rate = cost[INTER_OFFSET(this_mode)];
       int64_t dist;
 
       if (this_mode == NEWMV) {