net: stmmac: remove priv->eee_tw_timer

net: stmmac: remove priv->eee_tw_timer

priv->eee_tw_timer is only assigned during initialisation to a
constant value (STMMAC_DEFAULT_TWT_LS) and then never changed.

Remove priv->eee_tw_timer, and instead use STMMAC_DEFAULT_TWT_LS
for both uses in stmmac_eee_init().

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Choong Yong Liang <yong.liang.choong@linux.intel.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1tVZEG-0002Kk-VH@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>