watchdog: rt2880_wdt: minor clean up

Replace device_reset() with devm_reset_control_get() + reset_control_deassert().
Make use of watchdog_init_timeout() instead of setting the timeout manually.

Signed-off-by: John Crispin <blogic@openwrt.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>