Rename the function rd_pick_best_sub8x8_mode()

This large function is solely used for the RDO search for
inter prediction mode. It would be helpful for readers if its name
tells that whole function is used for inter mode decision only.

Change-Id: Ida366b142b7129bf89498227d186c54341c3af5e

av1/encoder/rdopt.c

@@ -5060,7 +5060,7 @@ static void joint_motion_search(const AV1_COMP *cpi, MACROBLOCK *x,
   }
 }
 
-static int64_t rd_pick_best_sub8x8_mode(
+static int64_t rd_pick_inter_best_sub8x8_mode(
     const AV1_COMP *const cpi, MACROBLOCK *x, int_mv *best_ref_mv,
     int_mv *second_best_ref_mv, int64_t best_rd, int *returntotrate,
     int *returnyrate, int64_t *returndistortion, int *skippable, int64_t *psse,
@@ -10878,7 +10878,7 @@ void av1_rd_pick_inter_mode_sub8x8(const struct AV1_COMP *cpi,
 #else
             mbmi->interp_filter = switchable_filter_index;
 #endif
-            tmp_rd = rd_pick_best_sub8x8_mode(
+            tmp_rd = rd_pick_inter_best_sub8x8_mode(
                 cpi, x, &mbmi_ext->ref_mvs[ref_frame][0], second_ref, best_yrd,
                 &rate, &rate_y, &distortion, &skippable, &total_sse,
                 (int)this_rd_thresh, seg_mvs,
@@ -10957,7 +10957,7 @@ void av1_rd_pick_inter_mode_sub8x8(const struct AV1_COMP *cpi,
       if (!pred_exists) {
         // Handles the special case when a filter that is not in the
         // switchable list (bilinear) is indicated at the frame level
-        tmp_rd = rd_pick_best_sub8x8_mode(
+        tmp_rd = rd_pick_inter_best_sub8x8_mode(
             cpi, x, &x->mbmi_ext->ref_mvs[ref_frame][0], second_ref, best_yrd,
             &rate, &rate_y, &distortion, &skippable, &total_sse,
             (int)this_rd_thresh, seg_mvs,