Tweak to manual move eindex arg

Marlin/src/lcd/ultralcd.cpp

    */
   inline void manual_move_to_current(AxisEnum axis
     #if E_MANUAL > 1
-      , int8_t eindex=-1
+      , const int8_t eindex=-1
     #endif
   ) {
     #if ENABLED(DUAL_X_CARRIAGE) || E_MANUAL > 1
   void lcd_move_z() { _lcd_move_xyz(PSTR(MSG_MOVE_Z), Z_AXIS); }
   void _lcd_move_e(
     #if E_MANUAL > 1
-      int8_t eindex=-1
+      const int8_t eindex=-1
     #endif
   ) {
     if (use_click()) { return lcd_goto_previous_menu(); }