kernfs: fix missing kernfs_idr_lock to remove an ID from the IDR

The root->ino_idr is supposed to be protected by kernfs_idr_lock, fix
it.

Fixes: 488dee96 ("kernfs: allow creating kernfs objects with arbitrary uid/gid")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20230523024017.24851-1-songmuchun@bytedance.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>