Fix a compiler warning.  No functional change.

* subversion/libsvn_subr/checksum.c
  (svn_checksum_parse_hex): Use apr_size_t instead of int to be consistent with
    size returned from DIGESTSIZE(), which is just a handy way of getting
    data from the digest_sizes array.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1569659 13f79535-47bb-0310-9956-ffa450edef68