md/raid10: clean up md_add_new_disk()

Commit 1a855a06 ("md: fix bug with re-adding of partially recovered
device.") only add device which is set to In_sync. But it let devices
without metadata cannot be added when they should be.

Commit bf572541 ("md: fix regression with re-adding devices to arrays
with no metadata") fix the above issue, it set device without metadata to
In_sync when add new disk.

However, after commit f466722c ("md: Change handling of save_raid_disk
and metadata update during recovery.") deletes changes of the first patch,
setting In_sync for devcie without metadata is meanless because the flag
will be cleared soon and will not be used during this period. Clean it up.

Signed-off-by: Li Nan <linan122@huawei.com>
Reviewed-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20230527101851.3266500-2-linan666@huaweicloud.com