ptrace: __ptrace_unlink: use the ptrace_reparented() helper

Currently __ptrace_unlink() checks list_empty(->ptrace_list) to figure out
whether the child was reparented.  Change the code to use ptrace_reparented()
to make this check more explicit and consistent.

No functional changes.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/ptrace.c

@@ -73,7 +73,7 @@ void __ptrace_unlink(struct task_struct *child)
 	BUG_ON(!child->ptrace);
 
 	child->ptrace = 0;
-	if (!list_empty(&child->ptrace_list)) {
+	if (ptrace_reparented(child)) {
 		list_del_init(&child->ptrace_list);
 		remove_parent(child);
 		child->parent = child->real_parent;