net: stmmac: mediatek: stop initialising plat->mac_interface

Mediatek doesn't make use of mac_interface, and none of the in-tree
DT files use the mac-mode property. Therefore, mac_interface already
follows phy_interface. Remove this unnecessary assignment.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/E1u4zyh-000xVE-PG@rmk-PC.armlinux.org.uk


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