md: revert io stats accounting

mainline inclusion
from mainline-v5.14-rc1
commit ad3fc798
category: bugfix
bugzilla: 169402 https://gitee.com/openeuler/kernel/issues/I4DDEL

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ad3fc798800fb7ca04c1dfc439dba946818048d8

-------------------------------------------------

The commit 41d2d848 ("md: improve io stats accounting") could cause
double fault problem per the report [1], and also it is not correct to
change ->bi_end_io if md don't own it, so let's revert it.

And io stats accounting will be replemented in later commits.

[1]. https://lore.kernel.org/linux-raid/3bf04253-3fad-434a-63a7-20214e38cf26@gmail.com/T/#t



Fixes: 41d2d848 ("md: improve io stats accounting")
Signed-off-by: Guoqing Jiang <jiangguoqing@kylinos.cn>
Signed-off-by: Song Liu <song@kernel.org>
Signed-off-by: Luo Meng <luomeng12@huawei.com>

Conflicts:
	drivers/md/md.c
Reviewed-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>