Follow-up to r1547137.

* subversion/tests/libsvn_fs_fs/fs-fs-pack-test.c
  (create_packed_filesystem): Return a proper error object instead of a constant.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1547145 13f79535-47bb-0310-9956-ffa450edef68