Fix a minor compile warning

Marlin/src/gcode/config/M200-M205.cpp

 
   LOOP_XYZE(i) {
     if (parser.seen(axis_codes[i])) {
-      const uint8_t a = (i == uint8_t(E_AXIS) ? E_AXIS_N(target_extruder) : i);
+      const uint8_t a = (i == E_AXIS ? E_AXIS_N(target_extruder) : i);
       planner.settings.max_acceleration_mm_per_s2[a] = parser.value_axis_units((AxisEnum)a);
     }
   }

Marlin/src/inc/Conditionals_LCD.h

  */
 #if ENABLED(DISTINCT_E_FACTORS) && E_STEPPERS > 1
   #define XYZE_N (XYZ + E_STEPPERS)
-  #define E_AXIS_N(E) (E_AXIS + E)
+  #define E_AXIS_N(E) (uint8_t(E_AXIS) + E)
 #else
   #undef DISTINCT_E_FACTORS
   #define XYZE_N XYZE
-  #define E_AXIS_N(E) E_AXIS
+  #define E_AXIS_N(E) uint8_t(E_AXIS)
 #endif
 
 /**