ceph: use pathlen values returned by set_request_path_attr

We make copies of the dentry name in set_request_path_attr, but then
create_request_message re-fetches the lengths out of the dentry. While
we don't currently set the *_drop fields unless the parents are locked,
it's still better not to rely on that sort of implicit assumption.

Use the pathlen values that set_request_path_attr returned instead, as
they will always be correct for the returned paths themselves.

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