test_rgw_admin_log.cc: fix use-after-free

Fix for:

CID 1054876 (#1 of 1): Use after free (USE_AFTER_FREE)
 pass_freed_arg: Passing freed pointer bucket_obj as an
 argument to put_bucket_obj

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>