MIPS: dts: Boston: Fix PCI bus dtc warnings:

dtc recently (v1.4.4-8-g756ffc4f52f6) added PCI bus checks. Fix the
warnings now emitted:

arch/mips/boot/dts/img/boston.dtb: Warning (pci_bridge): /pci@10000000: missing bus-range for PCI bridge
arch/mips/boot/dts/img/boston.dtb: Warning (pci_bridge): /pci@12000000: missing bus-range for PCI bridge
arch/mips/boot/dts/img/boston.dtb: Warning (pci_bridge): /pci@14000000: missing bus-range for PCI bridge

Signed-off-by: Matt Redfearn <matt.redfearn@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Paul Burton <paul.burton@mips.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: linux-mips@linux-mips.org
Cc: devicetree@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/19070/
Signed-off-by: James Hogan <jhogan@kernel.org>