watchdog/softlockup: fix wrong output when watchdog_thresh < 3

watchdog/softlockup: fix wrong output when watchdog_thresh < 3

When watchdog_thresh is below 3, sample_period will be less than 1 second.
So the following output will print when softlockup:

CPU#3 Utilization every 0s during lockup

Fix this by changing time unit from seconds to milliseconds.

Link: https://lkml.kernel.org/r/20250812074132.27810-1-yaozhenguo@jd.com
Signed-off-by: ZhenguoYao <yaozhenguo1@gmail.com>
Cc: Bitao Hu <yaoma@linux.alibaba.com>
Cc: Li Huafei <lihuafei1@huawei.com>
Cc: Max Kellermann <max.kellermann@ionos.com>
Cc: Thomas Gleinxer <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>