drbd: use DEFINE_SPINLOCK() for spinlock

spinlock can be initialized automatically with DEFINE_SPINLOCK()
rather than explicitly calling spin_lock_init().

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Guobin Huang <huangguobin4@huawei.com>
Link: https://lore.kernel.org/r/1617710988-49205-1-git-send-email-huangguobin4@huawei.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>