Skip redundant initializations in av1_rd_pick_inter_mode()

In `av1_rd_pick_inter_mode()`, init_mbmi() and set_ref_ptrs() were
called unconditionally prior to mode evaluation. However, these
intializations are redundant when `is_skip_inter_mode` is true.
In this patch, init_mbmi() and set_ref_ptrs() are only called when
mode evaluation is not skipped.

This change is bit-exact for all presets.

Encoder performance results averaged over all resolutions:

       Encoder Instruction
  CPU   Count Reduction (%)
   1        0.33
   2        0.39
   3        0.70
   4        0.75
   5        0.77
   6        1.03

Change-Id: I88a5e027a1a41af8d9c0da45b5fb77897f27c14d

av1/encoder/rdopt.c

diff --git a/av1/encoder/rdopt.c b/av1/encoder/rdopt.c
index 7649035..dde46f6 100644
--- a/av1/encoder/rdopt.c
+++ b/av1/encoder/rdopt.c
@@ -6255,11 +6255,8 @@
         ref_frame > INTRA_FRAME && second_ref_frame == NONE_FRAME;
     const int comp_pred = second_ref_frame > INTRA_FRAME;
 
-    init_mbmi(mbmi, this_mode, ref_frames, cm);
-
     txfm_info->skip_txfm = 0;
     sf_args.num_single_modes_processed += is_single_pred;
-    set_ref_ptrs(cm, xd, ref_frame, second_ref_frame);
 #if CONFIG_COLLECT_COMPONENT_TIMING
     start_timing(cpi, skip_inter_mode_time);
 #endif
@@ -6271,6 +6268,9 @@
 #endif
     if (is_skip_inter_mode) continue;
 
+    init_mbmi(mbmi, this_mode, ref_frames, cm);
+    set_ref_ptrs(cm, xd, ref_frame, second_ref_frame);
+
     // Select prediction reference frames.
     for (i = 0; i < num_planes; i++) {
       xd->plane[i].pre[0] = yv12_mb[ref_frame][i];