ARM: dts: imx35: Remove invalid wdog property

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

Remove it to fix the following DT check warning:

watchdog@53fdc000: 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>