ARM: dts: mvebu: fix reference to a390 spi controller
The SPI controller in the arch/arm/boot/dts/armada-39x.dtsi file has moved
to a different location in the hierarchy, which breaks the overrides
in the board specific file:
Warning (reg_format): "reg" property in /soc/internal-regs/spi@10680/spi-flash@1 has invalid length (4 bytes) (#address-cells == 2, #size-cells == 1)
Warning (avoid_default_addr_size): Relying on default #address-cells value for /soc/internal-regs/spi@10680/spi-flash@1
This changes the board to reference the spi controller by its label
(which has not changed) rather than the full path.