dt-bindings: watchdog: toshiba,visconti-wdt: Update the common clock properties

The clock for this driver switched to the common clock controller driver.
Therefore, update common clock properties for watchdog in the binding document.
And this matched this example with the actual dts.

Signed-off-by: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@toshiba.co.jp>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20220525004605.2128727-1-nobuhiro1.iwamatsu@toshiba.co.jp


Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>