firmware: Call lv_disp_flush_ready() in vsync handler

firmware/main/lcd.c

@@ -45,6 +45,7 @@ static bool val_on_vsync(esp_lcd_panel_handle_t panel, const esp_lcd_rgb_panel_e
   }
 #endif
 
+  lv_disp_flush_ready(user_ctx);
   return high_task_awoken == pdTRUE;
 }
 
@@ -57,7 +58,6 @@ static void val_lvgl_flush_cb(lv_display_t *disp, const lv_area_t *area, uint8_t
 
   // pass the draw buffer to the driver
   esp_lcd_panel_draw_bitmap(panel_handle, area->x1, area->y1, area->x2 + 1, area->y2 + 1, px_map);
-  lv_disp_flush_ready(disp);
 }
 
 static void val_increase_lvgl_tick(void *arg) {