Fix compile error (macro substitution typo) (#16194)

Marlin/src/Marlin.cpp

         bool oldstatus;
         switch (active_extruder) {
           default:
-          #define _CASE_EN(N) case N: oldstatus = E##N_ENABLE_READ(); enable_E##N(); break;
+          #define _CASE_EN(N) case N: oldstatus = E##N##_ENABLE_READ(); enable_E##N(); break;
           REPEAT(E_STEPPERS, _CASE_EN);
         }
       #endif