hung_task: print message when hung_task_warnings gets down to zero.

It's useful to report it when hung_task_warnings gets down to zero, so
that we can know if kernel log was lost or there is no hung task was
detected.

Link: https://lkml.kernel.org/r/20230201135416.GA6560@didi-ThinkCentre-M920t-N000


Signed-off-by: fuyuanli <fuyuanli@didiglobal.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>