block: fix bad definition of BIO_RW_SYNC

We can't OR shift values, so get rid of BIO_RW_SYNC and use BIO_RW_SYNCIO
and BIO_RW_UNPLUG explicitly. This brings back the behaviour from before
213d9417fec62ef4c3675621b9364a667954d4dd.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/mm/page_io.c b/mm/page_io.c
index dc6ce0a..3023c47 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -111,7 +111,7 @@
 		goto out;
 	}
 	if (wbc->sync_mode == WB_SYNC_ALL)
-		rw |= (1 << BIO_RW_SYNC);
+		rw |= (1 << BIO_RW_SYNCIO) | (1 << BIO_RW_UNPLUG);
 	count_vm_event(PSWPOUT);
 	set_page_writeback(page);
 	unlock_page(page);