mediatek: filogic: fix mxl phy node dtc warnings

mediatek: filogic: fix mxl phy node dtc warnings

Add missing #address-cells and #size-cells to fix the
following dtc warnings:

mt7981-rfb-mxl-2p5g-phy-eth1.dtso:26.5-15: Warning (reg_format): /fragment@1/__overlay__/ethernet-phy@5:reg: property has invalid length (4 bytes) (#address-cells == 2, #size-cells == 1)
mt7981-rfb-mxl-2p5g-phy-swp5.dtso:27.5-15: Warning (reg_format): /fragment@1/__overlay__/ethernet-phy@5:reg: property has invalid length (4 bytes) (#address-cells == 2, #size-cells == 1)

Signed-off-by: Shiji Yang <yangshiji66@outlook.com>