Now that mddev_suspend() doean't rely on 'mddev->pers' to be set, it's
safe to remove such checking.

This will also allow the array to be suspended even before the array
is ran.
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20230825030956.1527023-7-yukuai1@huaweicloud.com