watchdog: mtx1-wdt: use devm_gpio_request_one()

Use devm_gpio_request_one() to make cleanup paths simpler.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>