The only way of stopping the watchdog is by resetting it.
Add the watchdog op for stopping the device and reset if
a reset line is provided.
At same time WDOG_HW_RUNNING should be remove from dw_wdt_start.
As commented by Guenter Roeck:
dw_wdt sets WDOG_HW_RUNNING in its open function. Result is
that the kref_get() in watchdog_open() won't be executed. But then
kref_put() in close will be called since the watchdog now does stop.
This causes the imbalance.