watchdog: bcm63xx_wdt: Remove unused field from bcm63xx_wdt_device

Field "default_ticks" is not used anywhere in the driver code.
This patch removes this field.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>