watchdog: Fix runtime PM imbalance on error

When watchdog_register_device() returns an error code,
a pairing runtime PM usage counter decrement is needed
to keep the counter balanced.

Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20200521080141.24373-1-dinghao.liu@zju.edu.cn


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