A source code style tweak.

* subversion/libsvn_subr/error.c
  (svn_error_symbolic_name): Use APR_SUCCESS instead of SVN_NO_ERROR as the
    constant for an (apr_status_t) no-error, like everywhere else.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1543216 13f79535-47bb-0310-9956-ffa450edef68