kernel/sys.c: k_getrusage() can use while_each_thread()

Change k_getrusage() to use while_each_thread(), no changes in the
compiled code.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Kees Cook <keescook@chromium.org>
Reviewed-by: Sameer Nanda <snanda@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/sys.c

@@ -1571,8 +1571,7 @@ static void k_getrusage(struct task_struct *p, int who, struct rusage *r)
 			t = p;
 			do {
 				accumulate_thread_rusage(t, r);
-				t = next_thread(t);
-			} while (t != p);
+			} while_each_thread(p, t);
 			break;
 
 		default: