Fix congestion_wait() sync/async vs read/write confusion

Commit 1faa16d22877f4839bd433547d770c676d1d964c accidentally broke
the bdi congestion wait queue logic, causing us to wait on congestion
for WRITE (== 1) when we really wanted BLK_RW_ASYNC (== 0) instead.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ad7cd1c..a35eeab 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1666,7 +1666,7 @@
 			preferred_zone, migratetype);
 
 		if (!page && gfp_mask & __GFP_NOFAIL)
-			congestion_wait(WRITE, HZ/50);
+			congestion_wait(BLK_RW_ASYNC, HZ/50);
 	} while (!page && (gfp_mask & __GFP_NOFAIL));
 
 	return page;
@@ -1831,7 +1831,7 @@
 	pages_reclaimed += did_some_progress;
 	if (should_alloc_retry(gfp_mask, order, pages_reclaimed)) {
 		/* Wait for some write requests to complete then retry */
-		congestion_wait(WRITE, HZ/50);
+		congestion_wait(BLK_RW_ASYNC, HZ/50);
 		goto rebalance;
 	}