block: free q->flush_rq in blk_init_allocated_queue error paths

Commit 7982e90c ("block: fix q->flush_rq NULL pointer crash on
dm-mpath flush") moved an allocation to blk_init_allocated_queue(), but
neglected to free that allocation on the error paths that follow.
Signed-off-by: Dave Jones <davej@fedoraproject.org>
Acked-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

block/blk-core.c

@@ -713,7 +713,7 @@ blk_init_allocated_queue(struct request_queue *q, request_fn_proc *rfn,
 		return NULL;
 
 	if (blk_init_rl(&q->root_rl, q, GFP_KERNEL))
-		return NULL;
+		goto fail;
 
 	q->request_fn		= rfn;
 	q->prep_rq_fn		= NULL;
@@ -737,12 +737,16 @@ blk_init_allocated_queue(struct request_queue *q, request_fn_proc *rfn,
 	/* init elevator */
 	if (elevator_init(q, NULL)) {
 		mutex_unlock(&q->sysfs_lock);
-		return NULL;
+		goto fail;
 	}
 
 	mutex_unlock(&q->sysfs_lock);
 
 	return q;
+
+fail:
+	kfree(q->flush_rq);
+	return NULL;
 }
 EXPORT_SYMBOL(blk_init_allocated_queue);