divide error in fbcon_switch

[syzbot]

syzbot suspects this issue was fixed by commit:

commit ce684552a266cb1c7cc2f7e623f38567adec6653
Author: Tetsuo Handa <penguin-kernel at I-love.SAKURA.ne.jp>
Date:   Sun Jul 12 11:10:12 2020 +0000

    vt: Reject zero-sized screen buffer size.

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=155549c4900000
start commit:   76bb8b05 Merge tag 'kbuild-v5.5' of git://git.kernel.org/p..
git tree:       upstream
kernel config:  https://syzkaller.appspot.com/x/.config?x=dd226651cb0f364b
dashboard link: https://syzkaller.appspot.com/bug?extid=13013adc4a234406c29e
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17d69aeae00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13fdcc2ae00000

If the result looks correct, please mark the issue as fixed by replying with:

#syz fix: vt: Reject zero-sized screen buffer size.

For information about bisection process see: https://goo.gl/tpsmEJ#bisection