Change break statement in a 2d loop to a return statement.

The break statement only breaks out of the nested loop, not the
top-level loop, so it doesn't always work as intended. Changing it
to a return statement does what's intended.

Change-Id: I585419823b39a04ec8826b1c8a216099b1728ba7

vp9/encoder/vp9_rdopt.c

@@ -1368,13 +1368,10 @@ static int64_t rd_pick_intra4x4mby_modes(VP9_COMP *cpi, MACROBLOCK *mb,
         mic->bmi[i + j].as_mode = best_mode;
 
       if (total_rd >= best_rd)
-        break;
+        return INT64_MAX;
     }
   }
 
-  if (total_rd >= best_rd)
-    return INT64_MAX;
-
   *Rate = cost;
   *rate_y = tot_rate_y;
   *Distortion = distortion;