net: stmmac: qcom-ethqos: remove speed_mode_2500() method

qcom-ethqos doesn't need to implement the speed_mode_2500() method as
it is only setting priv->plat->phy_interface to 2500BASE-X, which is
already a pre-condition for assigning speed_mode_2500 in
qcom_ethqos_probe(). So, qcom_ethqos_speed_mode_2500() has no effect.
Remove it.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/E1u3bYa-000EcW-H1@rmk-PC.armlinux.org.uk


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