Old pointers of sibling were not cleared

When adding sibling at the head of linked list, the head if pointing
to something in linked list was not updated, hence a loop was formed
in linked list

Element0 - First addition to linked list
Element1 - Has higher delay hence added to back
0 ->(next) 1
Element2 - Delay is same as Element0, hence should be sibling of 0
           Shall be added at head

Expected:
2    ------------->(next) 1
|(sibling)
0

Bug: (Resolved with this)
2    ------------->(next) 1
|(sibling)
0    ------------->(next) 1

If we add more elements and next pointer of sibling is updated, old
references will cause issues
Element3 added

Expected:
2    ------------->(next) 3  ------------->(next) 1
|(sibling)
0

Bug: (Resolved with this)
2    ------------->(next) 3  ------------->(next) 1
|(sibling)
0    ------------->(next) 1
***Both siblings here point to different next***

events/equeue/equeue.c

@@ -239,8 +239,8 @@ static int equeue_enqueue(equeue_t *q, struct equeue_event *e, unsigned tick)
         if (e->next) {
             e->next->ref = &e->next;
         }
-
         e->sibling = *p;
+        e->sibling->next = 0;
         e->sibling->ref = &e->sibling;
     } else {
         e->next = *p;