Fix lcd_wait_for_homing causing menu to block

As a showcase function for how to do waiting in the lcd menu, this function should be preserved.

Marlin/ultralcd.cpp

   inline void lcd_wait_for_homing() {
     no_reentrance = true;
     while (!axis_homed[X_AXIS] || !axis_homed[Y_AXIS] || !axis_homed[Z_AXIS]) idle();
-    no_reentrance = true;
+    no_reentrance = false;
   }
 
   void lcd_return_to_status() { lcd_goto_screen(lcd_status_screen); }