fs/proc/array.c: change do_task_stat() to use while_each_thread()

Change the remaining next_thread (ab)users to use while_each_thread().

The last user which should be changed is next_tid(), but we can't do this

__exit_signal() and complete_signal() are fine, they actually need
next_thread() logic.

This patch (of 3):

do_task_stat() can 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>
diff --git a/fs/proc/array.c b/fs/proc/array.c
index 554a0b2..656e401 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -444,8 +444,7 @@
 				min_flt += t->min_flt;
 				maj_flt += t->maj_flt;
 				gtime += task_gtime(t);
-				t = next_thread(t);
-			} while (t != task);
+			} while_each_thread(task, t);
 			min_flt += sig->min_flt;
 			maj_flt += sig->maj_flt;