watchdog: tangox: Print info message using pointer to platform device

The device pointer in struct watchdog_device should not be used by drivers
and may be removed in the near future. Use the platform device pointer for
info messages instead.

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