ARM: dts: renesas: r9a06g032: Fix UART dma channel order

ARM: dts: renesas: r9a06g032: Fix UART dma channel order

make dtbs_check:

    arch/arm/boot/dts/renesas/r9a06g032-rzn1d400-db.dtb: serial@50000000: dma-names:0: 'tx' was expected
	    from schema $id: http://devicetree.org/schemas/serial/snps-dw-apb-uart.yaml#
    arch/arm/boot/dts/renesas/r9a06g032-rzn1d400-db.dtb: serial@50000000: dma-names:1: 'rx' was expected
	    from schema $id: http://devicetree.org/schemas/serial/snps-dw-apb-uart.yaml#
    ...

The DT bindings specify a fixed order of the channels in the dmas and
dma-names properties, while the Linux driver does not care.
Get rid of the warnings by changing the order in the DTS to match the
bindings.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/bcb604ad6e567de4e0410756ba840c82a32ff7d3.1739525488.git.geert+renesas@glider.be