ceph: vet the target and parent inodes before updating dentry lease

In a later patch, we're going to need to allow ceph_fill_trace to
update the dentry's lease when the parent is not locked. This is
potentially racy though -- by the time we get around to processing the
trace, the parent may have already changed.

Change update_dentry_lease to take a ceph_vino pointer and use that to
ensure that the dentry's parent still matches it before updating the
lease.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Yan, Zheng <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>