mediatek: filogic: fix flash node name dtc warnings

mediatek: filogic: fix flash node name dtc warnings

Correct dts node name based on reg property to fix the
following dtc warnings:

mt7981-rfb-spim-nand.dtso:20.25-67.6: Warning (spi_bus_reg): /fragment@1/__overlay__/spi_nand@0: SPI bus unit address format error, expected "1"
mt7986a-rfb-spim-nand.dts:41.23-76.4: Warning (spi_bus_reg): /soc/spi@1100a000/spi_nand@0: SPI bus unit address format error, expected "1"
../dts/mt7981a-comfast-cf-e393ax.dts:135.23-206.4: Warning (spi_bus_reg): /soc/spi@1100a000/spi_nand@0: SPI bus unit address format error, expected "1"
../dts/mt7981b-openwrt-one.dts:305.10-342.4: Warning (spi_bus_reg): /soc/spi@1100a000/flash@0: SPI bus unit address format error, expected "1"
../dts/mt7986a-zyxel-ex5601-t0-common.dtsi:166.30-180.4: Warning (spi_bus_reg): /soc/spi@1100a000/spi_nand@0: SPI bus unit address format error, expected "1"

Signed-off-by: Shiji Yang <yangshiji66@outlook.com>