fix(fs): add lv_fs_dir_t to lv_fs.h (#6925)

src/misc/lv_types.h

@@ -139,7 +139,7 @@ typedef struct lv_fs_file_cache_t lv_fs_file_cache_t;
 
 typedef struct lv_fs_path_ex_t lv_fs_path_ex_t;
 
-typedef struct lv_image_decoder_args_t lv_image_decoder_args_t;
+typedef struct _lv_image_decoder_args_t lv_image_decoder_args_t;
 
 typedef struct lv_image_cache_data_t lv_image_cache_data_t;