md/raid1: prioritize adding disk to 'removed' mirror

New disk should be added to "removed" position first instead of to be a
replacement. Commit 6090368a ("md/raid10: prioritize adding disk to
'removed' mirror") has fixed this issue for raid10. Fix it for raid1 now.

Signed-off-by: Li Nan <linan122@huawei.com>
Reviewed-by: Yu Kuai <yukuai3@huawei.com>
Link: https://lore.kernel.org/r/20230627014332.3810102-1-linan666@huaweicloud.com


Signed-off-by: Song Liu <song@kernel.org>