mips: lantiq: danube: add missing device_type in pci node

This fixes the following warning:
arch/mips/boot/dts/lantiq/danube_easy50712.dtb: pci@e105400 (lantiq,pci-xway): 'device_type' is a required property
	from schema $id: http://devicetree.org/schemas/pci/pci-bus-common.yaml#

Signed-off-by: Aleksander Jan Bajkowski <olek2@wp.pl>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

Author: abajk

arch/mips/boot/dts/lantiq/danube.dtsi

@@ -104,6 +104,8 @@
 				  0x1000000 0 0x00000000 0xae00000 0 0x200000>; /* io space */
 			reg = <0x7000000 0x8000		/* config space */
 				0xe105400 0x400>;	/* pci bridge */
+
+			device_type = "pci";
 		};
 	};
 };