md-bitmap: suspend array earlier in location_store()

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

This will also be helper to refactor mddev_suspend() later.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20230825030956.1527023-6-yukuai1@huaweicloud.com