ARM: dts: vfxxx: Remove invalid wdog property

The 'clock-names' property is not a valid property for wdog.

Remove it to fix the following DT check warning:

vf610-zii-ssmb-dtu.dtb: watchdog@4003e000: Unevaluated properties are not allowed ('clock-names' was unexpected)
From schema: /Documentation/devicetree/bindings/watchdog/fsl-imx-wdt.yaml

Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>