ramips: mt7621-dts: fix switch@1f warnings

ramips: mt7621-dts: fix switch@1f warnings

Remove reg property from ports node to fix this warning:

Warning (unit_address_vs_reg): /ethernet@1e100000/mdio-bus/switch@1f/ports: node has a reg or ranges property, but no unit name

Another warning surfaces afterwards. Remove #address-cells and #size-cells
from switch@1f node to fix this warning:

Warning (avoid_unnecessary_addr_size): /ethernet@1e100000/mdio-bus/switch@1f: unnecessary #address-cells/#size-cells without "ranges" or child "reg" property

Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>