We were using sys_slist_remove() to remove object, object instance and
observer w/o passing the previous sys_snode_t to it (NULL).
This will instruct the function to treat the node as the list head and
result in unexpected behavior after the removal.
Correct it by using sys_slist_find_and_remove() or passing the previous
node to the function.
Signed-off-by: Robert Chou <robert.ch.chou@acer.com>
b6a0cdfd64