Fix panic upon cancelling not scheduled task

Calling zephyr_ll_task_cancel() for a task which was actually never
scheduled results later in panic in zephyr_ll_task_done().

The fix makes zephyr_ll_task_cancel() do nothing for tasks which were
only initialized but never scheduled.

Signed-off-by: Serhiy Katsyuba <serhiy.katsyuba@intel.com>

src/schedule/zephyr_ll.c

@@ -436,11 +436,18 @@ static int zephyr_ll_task_cancel(void *data, struct task *task)
  * kept atomic, so we have to lock here too.
  */
  zephyr_ll_lock(sch, &flags);
- if (task->state != SOF_TASK_STATE_FREE) {
+
+ /*
+ * SOF_TASK_STATE_CANCEL can only be assigned to a task which is on scheduler's list.
+ * Later such task will be removed from the list by zephyr_ll_task_done(). Do nothing
+ * for tasks which were never scheduled or were already removed from scheduler's list.
+ */
+ if (task->state != SOF_TASK_STATE_INIT && task->state != SOF_TASK_STATE_FREE) {
  task->state = SOF_TASK_STATE_CANCEL;
  /* let domain know that a task has been cancelled */
  domain_task_cancel(sch->ll_domain, task);
  }
+
  zephyr_ll_unlock(sch, &flags);
 
  return 0;