Branch and cache miss speedups

Just some low hanging fruit.

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/io_u.c b/io_u.c
index a69efb7..77557df 100644
--- a/io_u.c
+++ b/io_u.c
@@ -1307,9 +1307,9 @@
 	else if (!queue_full(td)) {
 		io_u = io_u_qpop(&td->io_u_freelist);
 
+		io_u->file = NULL;
 		io_u->buflen = 0;
 		io_u->resid = 0;
-		io_u->file = NULL;
 		io_u->end_io = NULL;
 	}