Copter: integrate AC_WPNav get_speed_xy name change

ArduCopter/ArduCopter.pde

@@ -1448,7 +1448,7 @@ static void tuning(){
 
     case CH6_WP_SPEED:
         // set waypoint navigation horizontal speed to 0 ~ 1000 cm/s
-        wp_nav.set_horizontal_velocity(g.rc_6.control_in);
+        wp_nav.set_speed_xy(g.rc_6.control_in);
         break;
 
     // Acro roll pitch gain

ArduCopter/commands_logic.pde

@@ -794,7 +794,7 @@ static bool do_guided(const AP_Mission::Mission_Command& cmd)
 static void do_change_speed(const AP_Mission::Mission_Command& cmd)
 {
     if (cmd.content.speed.target_ms > 0) {
-        wp_nav.set_horizontal_velocity(cmd.content.speed.target_ms * 100.0f);
+        wp_nav.set_speed_xy(cmd.content.speed.target_ms * 100.0f);
     }
 }