md/raid10: submit bio directly to replacement disk

commit 6d399783e9d4e9bd44931501948059d24ad96ff8 upstream.

Commit 57c67df4(md/raid10: submit IO from originating thread instead of
md thread) submits bio directly for normal disks but not for replacement
disks. There is no point we shouldn't do this for replacement disks.

Cc: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>