block: fix return value on cfq_init() failure

cfq_init() would return zero after kmem cache creation failure.  Fix
so that it returns -ENOMEM.
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/cfq-iosched.c

@@ -4202,6 +4202,7 @@ static int __init cfq_init(void)
 	if (ret)
 		return ret;
 
+	ret = -ENOMEM;
 	cfq_pool = KMEM_CACHE(cfq_queue, 0);
 	if (!cfq_pool)
 		goto err_pol_unreg;