vt_kdsetmode: extend console locking

stable inclusion
from linux-4.19.206
commit 0776c1a20babb4ad0b7ce7f2f4e0806a97663187
CVE: CVE-2021-3753

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

commit 2287a51b upstream.

As per the long-suffering comment.

Reported-by: Minh Yuan <yuanmingbuaa@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jirislaby@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>