Incorrect padding in ztypes_freebsd_amd64.go

https://github.com/creack/pty/blob/8ab47f72e8547a066b4ea926f4523775bc1a0ec2/ztypes_freebsd_amd64.go#L12

Should be just

```go
type fiodgnameArg struct {
        Len     int32
        Buf     *byte
}
```

according to `go tool cgo -godefs types_freebsd.go`