libseccomp: Fix install option order

Commit ca0e5152 introduced a bad option order, leading to another build
failure.

Fixes
http://autobuild.buildroot.org/results/0e7de5e7c792b5ef195ee98fe1e7bb1c6b220bfb/build-end.log



Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>