stepper: Reset the next step time on a stepper stop

Automatically reset the next step time to zero on a stepper_stop()
call.  This makes the host code simpler as it no longer needs to
schedule an explicit reset_step_clock command on the step after a
homing operation.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/stepper.c

@@ -238,6 +238,7 @@ void
 stepper_stop(struct stepper *s)
 {
     sched_del_timer(&s->time);
+    s->next_step_time = 0;
     s->position = -stepper_get_position(s);
     s->count = 0;
     s->flags &= SF_INVERT_STEP;