perl-net-ssleay: fix build

the new option OPTIMIZE needs the same replacement.

see http://autobuild.buildroot.net/results/278f9d121273a16cedc009c0b8df0a8659d8fb73/

Signed-off-by: Francois Perrad <francois.perrad@gadz.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>