watchdog: cadence_wdt: fix timeout setting

wdt_timeout must not be initialized to CDNS_WDT_DEFAULT_TIMEOUT in
order to allow the value to be overriddden by a device tree setting.

This way, the default timeout value will be used only in case module_param
has not been set, or device tree timeout-sec has not been defined.

Signed-off-by: Tomas Melin <tomas.melin@vaisala.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>