Planning: reduced s number in st_graph to avoid too much computation time.

Author: lianglia-apollo

modules/planning/conf/planning_config.pb.txt

@@ -36,7 +36,7 @@ em_planner_config {
     dp_st_speed_config {
         total_path_length: 150
         total_time: 8.0
-        matrix_dimension_s: 400
+        matrix_dimension_s: 150
         matrix_dimension_t: 8
 
         speed_weight: 0.0