opp: use list_del_init instead of list_del/INIT_LIST_HEAD

Using list_del_init() instead of list_del() + INIT_LIST_HEAD()
to simpify the code.

Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>