ovl: expand warning in ovl_d_real()

stable inclusion
from stable-5.10.17
commit e5c376c41a5798451355fb2e0732847be4a64c58
bugzilla: 48169

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

commit cef4cbff upstream.

There was a syzbot report with this warning but insufficient information...

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Acked-by: Xie XiuQi <xiexiuqi@huawei.com>