watchdog: use timeout_add_sec(9)

[Klemens Nanni]

Simple reduction here as done in many other places, tested on an ARMv7
BeagleBone Black with

        omdog0 at simplebus0 rev 0.1

        # sysctl kern.watchdog.period=3
        # sysctl kern.watchdog.auto=0

which reliably reboots the system after the specified amount of time.

OK?

Index: kern/kern_watchdog.c
===================================================================
RCS file: /cvs/src/sys/kern/kern_watchdog.c,v
retrieving revision 1.13
diff -u -p -r1.13 kern_watchdog.c
--- kern/kern_watchdog.c        9 Jan 2017 17:58:44 -0000       1.13
+++ kern/kern_watchdog.c        15 Jun 2019 23:42:24 -0000
@@ -54,7 +54,7 @@ wdog_tickle(void *arg)
        if (wdog_ctl_cb == NULL)
                return;
        (void) (*wdog_ctl_cb)(wdog_ctl_cb_arg, wdog_period);
-       timeout_add(&wdog_timeout, wdog_period * hz / 2);
+       timeout_add_sec(&wdog_timeout, wdog_period / 2);
 }
 
 void
@@ -100,7 +100,7 @@ sysctl_wdog(int *name, u_int namelen, vo
 
        if (wdog_auto && wdog_period > 0) {
                (void) (*wdog_ctl_cb)(wdog_ctl_cb_arg, wdog_period);
-               timeout_add(&wdog_timeout, wdog_period * hz / 2);
+               timeout_add_sec(&wdog_timeout, wdog_period / 2);
        } else
                timeout_del(&wdog_timeout);