md: Make bio_alloc_mddev use bio_alloc_bioset

bio_alloc_bioset returns a bio pointer or NULL, so we can avoid storing
the returned data into a new variable.
Acked-by: Guoqing Jiang <gqjiang@suse.com>
Acked-by: Artur Paszkiewicz <artur.paszkiewicz@intel.com>
Signed-off-by: Marcos Paulo de Souza <marcos.souza.org@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/md/md.c

@@ -207,15 +207,10 @@ static bool create_on_open = true;
 struct bio *bio_alloc_mddev(gfp_t gfp_mask, int nr_iovecs,
 			    struct mddev *mddev)
 {
-	struct bio *b;
-
 	if (!mddev || !bioset_initialized(&mddev->bio_set))
 		return bio_alloc(gfp_mask, nr_iovecs);
 
-	b = bio_alloc_bioset(gfp_mask, nr_iovecs, &mddev->bio_set);
-	if (!b)
-		return NULL;
-	return b;
+	return bio_alloc_bioset(gfp_mask, nr_iovecs, &mddev->bio_set);
 }
 EXPORT_SYMBOL_GPL(bio_alloc_mddev);