softlockup: fix to allow compiling with !DETECT_HUNG_TASK

Fixes the following compile error:

 kernel/fork.c:1049: error: 'struct task_struct' has no member named 'last_switch_count'
 kernel/fork.c:1050: error: 'struct task_struct' has no member named 'last_switch_timestamp'

Signed-off-by: Mandeep Singh Baines <msb@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/fork.c

@@ -1041,7 +1041,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 
 	p->default_timer_slack_ns = current->timer_slack_ns;
 
-#ifdef CONFIG_DETECT_SOFTLOCKUP
+#ifdef CONFIG_DETECT_HUNG_TASK
 	p->last_switch_count = 0;
 	p->last_switch_timestamp = 0;
 #endif