Fix compile error with char LCD

Marlin/src/lcd/ultralcd.cpp

@@ -4861,7 +4861,9 @@ void kill_screen(const char* lcd_msg) {
       encoderTopLine = 0;
       encoderPosition = 2 * ENCODER_STEPS_PER_MENU_ITEM;
       screen_changed = true;
-      first_page = false;
+      #if ENABLED(DOGLCD)
+        first_page = false;
+      #endif
       lcdDrawUpdate = LCDVIEW_CLEAR_CALL_REDRAW;
     }