net: fec: use phydev->eee_cfg.tx_lpi_timer

net: fec: use phydev->eee_cfg.tx_lpi_timer

Rather than maintaining a private copy of the LPI timer, make use of
the LPI timer maintained by phylib. In any case, phylib overwrites the
value of tx_lpi_timer set by the driver in phy_ethtool_get_eee().

Note that feb->eee.tx_lpi_timer is initialised to zero, which is just
the same with phylib's copy, so there should be no functional change.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Tested-by: Wei Fang <wei.fang@nxp.com>
Link: https://patch.msgid.link/E1tKzVS-006c67-IJ@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>