rtc: stmp3xxx: Don't reset the rtc in .probe() when watchdog is running

As pointed out in the added comment resetting the rtc also stops the
included watchdog. This is bad if the bootloader started the watchdog to
secure the boot process. So don't reset if the watchdog is running.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>