Refactor edf_sched to align with embedded node

The condition check is removed because the node is embedded in the tcb,
no need to confirm whether tcb is existing anymore.

The access of tcb_t is replaced by the marco to align with the embedded
node design.

Author: vicLin8712

app/rtsched.c

@@ -404,12 +404,7 @@ static int32_t edf_sched(void)
     /* Scan all tasks to find the one with earliest deadline */
     list_node_t *node = list_next(kcb->tasks->head);
     while (node && node != kcb->tasks->tail) {
-        if (!node->data) {
-            node = list_next(node);
-            continue;
-        }
-
-        tcb_t *task = (tcb_t *) node->data;
+        tcb_t *task = tcb_from_global_node(node);
 
         /* Consider both READY and RUNNING RT tasks for preemptive scheduling */
         if ((task->state == TASK_READY || task->state == TASK_RUNNING) &&