CVE-2021-47579 ovl: fix warning in ovl_create_real()

In the Linux kernel, the following vulnerability has been resolved: ovl: fix warning in ovlcreatereal Syzbot triggered the following warning in ovlworkdircreate - ovlcreatereal: if !err && WARNON!newdentry-dinode The reason is that the cgroup2 filesystem returns from mkdir without instantiating t...