arm64: dts: ls208xa-qds: Pass unit name to dspi child nodes

Pass unit name to dspi child nodes to fix the following build warnings
with W=1:

arch/arm64/boot/dts/freescale/fsl-ls2080a-qds.dtb: Warning (unit_address_vs_reg): Node /soc/dspi@2100000/n25q128a has a reg or ranges property, but no unit name
arch/arm64/boot/dts/freescale/fsl-ls2080a-qds.dtb: Warning (unit_address_vs_reg): Node /soc/dspi@2100000/sst25wf040b has a reg or ranges property, but no unit name
arch/arm64/boot/dts/freescale/fsl-ls2080a-qds.dtb: Warning (unit_address_vs_reg): Node /soc/dspi@2100000/en25s64 has a reg or ranges property, but no unit name

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>