net: phylink: clean the pcs_get_state documentation

commit 4d72c3bb

 ("net: phylink: strip out pre-March 2020 legacy code")
dropped the mac_pcs_get_state ops in phylink_mac_ops in favor of
dedicated PCS operation pcs_get_state. However, the documentation for
the pcs_get_state ops was incorrectly converted and now self-references.

Drop the extra comment.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>