net: stmmac: remove unnecessary checks in ethtool eee ops

net: stmmac: remove unnecessary checks in ethtool eee ops

Phylink will check whether the MAC supports the LPI methods in
struct phylink_mac_ops, and return -EOPNOTSUPP if the LPI capabilities
are not provided. stmmac doesn't provide LPI capabilities if
priv->dma_cap.eee is not set.

Therefore, checking the state of priv->dma_cap.eee in the ethtool ops
and returning -EOPNOTSUPP is redundant - let phylink handle this.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1umsf0-008vKK-A3@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>