fixed timep handling in time()

With the original time.s, the following code (on C64):

    #include <stdio.h>
    #include <time.h>
    time_t _systime(void) {
        return 999;
    }
    void main(void) {
        time_t t0 = 100, t1 = 200;
        t0 = time(&t1);
        printf("%ld %ld\n", t0, t1);
    }

leaves t1 unchanged.