ARM: dts: renesas: Fix DA9063 watchdog subnode names

make dtbs_check:

    arch/arm/boot/dts/r8a7791-koelsch-single-memory-node.dtb: pmic@58: 'wdt' does not match any of the regexes: 'pinctrl-[0-9]+'
	    From schema: Documentation/devicetree/bindings/mfd/dlg,da9063.yaml
    ...

Change the watchdog child node names to match the DA9063 DT bindings and
the Generic Names Recommendation in the Devicetree Specification.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/1dafdce285f7d14bec9e2033ac87fb30135895db.1655818230.git.geert+renesas@glider.be