raid5: avoid unnecessary bio data set

bio_reset doesn't change bi_io_vec and bi_max_vecs, so we don't need to
set them every time. bi_private will be set before the bio is
dispatched.
Signed-off-by: Shaohua Li <shli@fb.com>

drivers/md/raid5.c

@@ -2005,7 +2005,12 @@ static struct stripe_head *alloc_stripe(struct kmem_cache *sc, gfp_t gfp,
 			struct r5dev *dev = &sh->dev[i];
 
 			bio_init(&dev->req);
+			dev->req.bi_io_vec = &dev->vec;
+			dev->req.bi_max_vecs = 1;
+
 			bio_init(&dev->rreq);
+			dev->rreq.bi_io_vec = &dev->rvec;
+			dev->rreq.bi_max_vecs = 1;
 		}
 	}
 	return sh;
@@ -2507,14 +2512,6 @@ static void raid5_build_block(struct stripe_head *sh, int i, int previous)
 {
 	struct r5dev *dev = &sh->dev[i];
 
-	dev->req.bi_io_vec = &dev->vec;
-	dev->req.bi_max_vecs = 1;
-	dev->req.bi_private = sh;
-
-	dev->rreq.bi_io_vec = &dev->rvec;
-	dev->rreq.bi_max_vecs = 1;
-	dev->rreq.bi_private = sh;
-
 	dev->flags = 0;
 	dev->sector = raid5_compute_blocknr(sh, i, previous);
 }