package/refpolicy: fix build with ftp

Fix build failure raised since commit
61a47bb1

Fixes:
 - http://autobuild.buildroot.org/results/bde34d81a04b5ea96722dc56249089dce7e65b74



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>