syscall: fix linux amd64 build

TBR=rsc

TBR=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/100500047

src/pkg/syscall/syscall_linux_amd64.go

@@ -73,10 +73,10 @@ func Time(t *Time_t) (tt Time_t, err error) {
 	var tv Timeval
 	errno := gettimeofday(&tv)
 	if errno != 0 {
-		return errno
+		return 0, errno
 	}
 	if t != nil {
-		*t = tv.Sec
+		*t = Time_t(tv.Sec)
 	}
 	return Time_t(tv.Sec), nil
 }