WARNING in ext4_da_update_reserve_space

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger crash:

Reported-and-tested-by: syzbot+67e4f16db666b1c8253c at syzkaller.appspotmail.com

Tested on:

commit:         54d3adbc ext4: save all error info in save_error_info() an..
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4.git dev
kernel config:  https://syzkaller.appspot.com/x/.config?x=4527d1e2fb19fd5c
dashboard link: https://syzkaller.appspot.com/bug?extid=67e4f16db666b1c8253c
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)

Note: testing is done by a robot and is best-effort only.