fix build error

[yetist]

Fix the follow build errors:

cos_c_sdk/cos_multipart.c:892:10: 错误：implicit declaration of function ‘object_key_simplify_check’; did you mean ‘set_object_key
_simplify_check’? [-Wimplicit-function-declaration]
  892 |     if (!object_key_simplify_check(object->data)){
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~
      |          set_object_key_simplify_check

cos_c_sdk_test/cos_demo.c:1092:62: 错误：传递‘cos_download_part_to_file’的第 4 个参数时在不兼容的指针类型间转换 [-Wincompatible-pointer-types]
 1092 |     s = cos_download_part_to_file(options, &bucket, &object, &filepath, &resp_headers);
      |                                                              ^~~~~~~~~
      |                                                              |
      |                                                              cos_string_t *