ARM: dts: vf: align watchdog node name with dtschema

The dtschema expects watchdog device node name to be "watchdog":

  arch/arm/boot/dts/vf500-colibri-eval-v3.dt.yaml: wdog@4003e000:
    $nodename:0: 'wdog@4003e000' does not match '^watchdog(@.*|-[0-9a-f])?$'

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>