zs_set_speed
if (zs_set_speed(cs, 1200)) { /* set 1200bps */
int zs_set_speed(struct zs_chanstate *, int);
error = zs_set_speed(cs, ospeed);
(void)zs_set_speed(cs, INIT_SPEED);
(void)zs_set_speed(cs, sc->sc_base.sc_bps);