scl/Makefile.am: Make sure the installed SCLs are user-rwable

When installing the SCLs, make sure they're both readable and writable
by the installing user. This fixes the case of make distcheck combined
with make uninstall, which had these dirs set to read-list only.

Reported-by: Attila Szalay <sasa@balabit.hu>
Signed-off-by: Gergely Nagy <algernon@balabit.hu>