drbd: Remove unneeded semicolon

Fixes coccicheck warning:

drivers/block/drbd/drbd_req.c:887:2-3: Unneeded semicolon

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>