Update EC_POINT_new.pod

CLA: trivial
fix typo:
EC_point2buf => EC_POINT_point2buf

Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5367)