net: dsa: mv88e6xxx: remove mv88e6xxx_get_mac_eee()

mv88e6xxx_get_mac_eee() is no longer called by the core DSA code.
Remove it.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1tUllK-007Uz9-D7@rmk-PC.armlinux.org.uk


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