s390/ap: remove unnecessary spin_lock_init()

The spinlock ap_poll_timer_lock is initialized statically. It is
unnecessary to initialize by spin_lock_init().

Signed-off-by: Qinglang Miao <miaoqinglang@huawei.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>