riscv: dts: microchip: mpfs: fix incorrect pcie child node name

Recent versions of dt-schema complain about the PCIe controller's child
node name:
arch/riscv/boot/dts/microchip/mpfs-icicle-kit.dtb: pcie@2000000000: Unevaluated properties are not allowed ('clock-names', 'clocks', 'legacy-interrupt-controller', 'microchip,axi-m-atr0' were unexpected)
            From schema: Documentation/devicetree/bindings/pci/microchip,pcie-host.yaml
Make the dts match the correct property name in the dts.

Fixes: 528a5b1f ("riscv: dts: microchip: add new peripherals to icicle kit device tree")
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>