sfc: Stop generating bogus events in tenxpress_check_hw()

mdio_clause45_links_ok() correctly checks efx_phy_mode_disabled(), so
tenxpress_link_ok() doesn't need to.

From: Steve Hodgson <shodgson@solarflare.com>
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>