net: phy: c45: use cached EEE advertisement in genphy_c45_ethtool_get_eee

Now that disabled EEE modes are considered when populating
advertising_eee, we can use this bitmap here instead of reading
the PHY register.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/e57ed3d4-d0bc-4f91-83f6-8f48dfb6d7d7@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>