writeback: fix initial dirty limit

The initial value of global_wb_domain.dirty_limit set by
writeback_set_ratelimit() is zeroed out by the memset in
wb_domain_init().

Signed-off-by: Rabin Vincent <rabin.vincent@axis.com>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page-writeback.c

@@ -2063,10 +2063,10 @@ static struct notifier_block ratelimit_nb = {
  */
 void __init page_writeback_init(void)
 {
+	BUG_ON(wb_domain_init(&global_wb_domain, GFP_KERNEL));
+
 	writeback_set_ratelimit();
 	register_cpu_notifier(&ratelimit_nb);
-
-	BUG_ON(wb_domain_init(&global_wb_domain, GFP_KERNEL));
 }
 
 /**