watchdog: imx2_wdt: also set wdog->timeout to new_timeout

Commit faad5de0 ("watchdog: imx2_wdt: convert to watchdog core api")
removes the custom ioctl function. The generic ioctl handler is not
setting the wdog->timeout to the new_timeout but handing this preset
value back to the userspace. This patch sets the new value in the
drivers set_timeout function to fix that problem.

Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>