ext4: fix ext4_error_err save negative errno into superblock

ext4: fix ext4_error_err save negative errno into superblock

Fix As write_mmp_block() so that it returns -EIO instead of 1, so that
the correct error gets saved into the superblock.

Cc: stable@kernel.org
Fixes: d24b85b1e620 ("ext4: save all error info in save_error_info() and drop ext4_set_errno()")
Reported-by: Liu Zhi Qiang <liuzhiqiang26@huawei.com>
Signed-off-by: Ye Bin <yebin10@huawei.com>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Link: https://lore.kernel.org/r/20210406025331.148343-1-yebin10@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>