mips: dts: ralink: mt7621: remove interrupt-parent from switch node

The interrupt-parent property is inherited from the ethernet node as it's a
parent node of the switch node. Therefore, remove the unnecessary
interrupt-parent property from the switch node.

Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Reviewed-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>