trivial: freebsd: remove unused variable
trivial: freebsd: remove unused variable

found by codacity

hughsie/fwupd,hughsie/fwupd,fwupd/fwupd,hughsie/fwupd,hughsie/fwupd,fwupd/fwupd,fwupd/fwupd,fwupd/fwupd