ovl: fix out of date comment and unreachable code

mainline inclusion
from mainline-v5.7-rc1
commit 735c907d
category: bugfix
bugzilla: NA
CVE: NA

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ovl_inode_update() is no longer called from create object code path.

Fixes: 01b39dcc ("ovl: use inode_insert5() to hash a newly...")
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Zheng Liang <zhengliang6@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>