Fix tool-change move with hotend offset (#15491)

Marlin/src/module/tool_change.cpp

       #endif
 
       #if HAS_HOTEND_OFFSET
-        xyz_pos_t diff = hotend_offset[new_tool];
+        xyz_pos_t diff = hotend_offset[new_tool] - hotend_offset[old_tool];
         #if ENABLED(DUAL_X_CARRIAGE)
           diff.x = 0;
         #endif