md/raid10: properly indicate failure when ending a failed write request

Similar to [1], this patch fixes the same bug in raid10. Also cleanup the
comments.

[1] commit 2417b986 ("md/raid1: properly indicate failure when ending
                         a failed write request")
Cc: stable@vger.kernel.org
Fixes: 7cee6d4e ("md/raid10: end bio when the device faulty")
Signed-off-by: Wei Shuyu <wsy@dogben.com>
Acked-by: Guoqing Jiang <jiangguoqing@kylinos.cn>
Signed-off-by: Song Liu <song@kernel.org>