Follow-up to r1588651: Missed one update causing crash.

* subversion/libsvn_fs_fs/caching.c
  (svn_fs_fs__initialize_caches): Another cache instance that need
                                  FS->POOL lifetime.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1588713 13f79535-47bb-0310-9956-ffa450edef68