ext4: use common helpers in all places reading metadata buffers

mainline inclusion
from mainline-5.10-rc1
commit 2d069c08
category: bugfix
bugzilla: 51832
CVE: NA
---------------------------

Revome all open codes that read metadata buffers, switch to use
ext4_read_bh_*() common helpers.

Signed-off-by: zhangyi (F) <yi.zhang@huawei.com>
Suggested-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20200924073337.861472-4-yi.zhang@huawei.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Conflicts:
	fs/ext4/balloc.c
	fs/ext4/inode.c
	fs/ext4/ialloc.c
	fs/ext4/inode.c

Signed-off-by: yangerkun <yangerkun@huawei.com>
Reviewed-by: zhangyi (F) <yi.zhang@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>