🩹 Fix MPC Edit Menu (#24059)

Followup to #23984

Co-authored-by: Scott Lahteine <thinkyhead@users.noreply.github.com>

Marlin/src/lcd/menu/menu_advanced.cpp

         #define MPC_EDIT_ITEMS(N) \
           _MPC_EDIT_ITEMS(N); \
           EDIT_ITEM_FAST_N(float43, N, MSG_MPC_AMBIENT_XFER_COEFF_FAN_E, &editable.decimal, 0, 1, []{ \
+            MPC_t &c = thermalManager.temp_hotend[MenuItemBase::itemIndex].constants; \
             c.fan255_adjustment = editable.decimal - c.ambient_xfer_coeff_fan0; \
           })
       #else
       #endif
 
       #if HAS_MULTI_HOTEND
-        auto mpc_edit_hotend = [&](const uint8_t e) {
+        static auto mpc_edit_hotend = [](const uint8_t e) {
           MPC_EDIT_DEFS(e);
           START_MENU();
           BACK_ITEM(MSG_TEMPERATURE);
           MPC_EDIT_ITEMS(e);
           END_MENU();
         };
-        #define MPC_ENTRY(N) SUBMENU_N(N, MSG_MPC_EDIT, [&]{ mpc_edit_hotend(MenuItemBase::itemIndex); });
+        #define MPC_ENTRY(N) SUBMENU_N(N, MSG_MPC_EDIT, []{ mpc_edit_hotend(MenuItemBase::itemIndex); });
       #else
         #define MPC_ENTRY MPC_EDIT_ITEMS
       #endif