net: pcs: pcs-lynx: use phylink_get_link_timer_ns() helper

Use the phylink_get_link_timer_ns() helper to get the period for the
link timer.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/E1pFyhW-0067jq-Fh@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>