watchdog: tangox: Set max_hw_heartbeat_ms instead of max_timeout

Setting max_hw_heartbeat_ms lets the watchdog core provide a virtual
timeout if the timeout requested by user space is larger than the maximum
hardware timeout. Also, it helps the watchdog core to provide heartbeats
if the hardware watchdog is running while closed.

Fixes: a3e376d2 ("watchdog: tangox: Mark running watchdog correctly")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>