devel/goswagger: Unbreak on aarch64

> Building swagger from ./cmd/swagger

golang.org/x/sys/unix

vendor/golang.org/x/sys/unix/ztypes_freebsd_arm64.go:400:12: undefined: uint128

http://thunderx1.nyi.freebsd.org/data/head-arm64-default/p518178_s355024/logs/errors/goswagger-0.21.0_1.log

Unbreak by updating golang.org/x/sys to 33540a1f6037 which adds support for
freebsd/arm64.