Fix some LVGL warnings

Marlin/src/lcd/extui/lib/mks_ui/draw_ui.cpp

@@ -400,7 +400,6 @@ void gcode_preview(char *path, int xpos_pixel, int ypos_pixel) {
     volatile uint16_t *p_index;
     //int res;
     char *cur_name;
-    uint16_t Color;
 
     cur_name = strrchr(path, '/');
     card.openFileRead(cur_name);

Marlin/src/lcd/extui/lib/mks_ui/tft_lvgl_configuration.cpp

@@ -590,7 +590,7 @@ unsigned int getTickDiff(unsigned int curTick, unsigned int lastTick) {
   #endif
 
   #if USE_XPT2046
-    #ifndef XPT2046_HOR_RES   480
+    #ifndef XPT2046_HOR_RES
       #define XPT2046_HOR_RES   480
     #endif
     #ifndef XPT2046_VER_RES