SCU firmware calculates pretimeout based on current time stamp
instead of watchdog timeout stamp, need to convert the pretimeout
to SCU firmware's timeout value.

Fixes: 15f7d7fc ("watchdog: imx_sc: Add pretimeout support")
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>