Follow-up to r1527103: fix a "shadow identifier" compiler warning.

* subversion/libsvn_subr/cache_config.c
  (svn_cache_config_get): rename POOL parameter

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1527105 13f79535-47bb-0310-9956-ffa450edef68