kthread: remove comments about old _do_fork() helper

The old _do_fork() helper has been removed in favor of kernel_clone().
Here correct some comments which still contain _do_fork()

Link: https://lore.kernel.org/r/20210111104807.18022-1-yanfei.xu@windriver.com
Cc: christian@brauner.io
Cc: linux-kernel@vger.kernel.org
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Yanfei Xu <yanfei.xu@windriver.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

include/trace/events/sched.h

@@ -366,7 +366,7 @@ TRACE_EVENT(sched_process_wait,
 );
 
 /*
- * Tracepoint for do_fork:
+ * Tracepoint for kernel_clone:
  */
 TRACE_EVENT(sched_process_fork,
 

kernel/kthread.c

@@ -294,7 +294,7 @@ static int kthread(void *_create)
 	do_exit(ret);
 }
 
-/* called from do_fork() to get node information for about to be created task */
+/* called from kernel_clone() to get node information for about to be created task */
 int tsk_fork_get_node(struct task_struct *tsk)
 {
 #ifdef CONFIG_NUMA