kernel/hung_task.c: set some hung_task.c variables storage-class-specifier to static

kernel/hung_task.c: set some hung_task.c variables storage-class-specifier to static

smatch reports several warnings
kernel/hung_task.c:31:19: warning:
  symbol 'sysctl_hung_task_check_count' was not declared. Should it be static?
kernel/hung_task.c:50:29: warning:
  symbol 'sysctl_hung_task_check_interval_secs' was not declared. Should it be static?
kernel/hung_task.c:52:19: warning:
  symbol 'sysctl_hung_task_warnings' was not declared. Should it be static?
kernel/hung_task.c:75:28: warning:
  symbol 'sysctl_hung_task_panic' was not declared. Should it be static?

These variables are only used in hung_task.c, so they should be static

Link: https://lkml.kernel.org/r/20230312164645.471259-1-trix@redhat.com
Signed-off-by: Tom Rix <trix@redhat.com>
Cc: Ben Dooks <ben.dooks@sifive.com>
Cc: fuyuanli <fuyuanli@didiglobal.com>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>