block: add blk_queue_dead()

There are a number of QUEUE_FLAG_DEAD tests.  Add blk_queue_dead()
macro and use it.

This patch doesn't introduce any functional difference.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index e7f9f65..f0b2ca8 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -425,7 +425,7 @@
 	if (!entry->show)
 		return -EIO;
 	mutex_lock(&q->sysfs_lock);
-	if (test_bit(QUEUE_FLAG_DEAD, &q->queue_flags)) {
+	if (blk_queue_dead(q)) {
 		mutex_unlock(&q->sysfs_lock);
 		return -ENOENT;
 	}
@@ -447,7 +447,7 @@
 
 	q = container_of(kobj, struct request_queue, kobj);
 	mutex_lock(&q->sysfs_lock);
-	if (test_bit(QUEUE_FLAG_DEAD, &q->queue_flags)) {
+	if (blk_queue_dead(q)) {
 		mutex_unlock(&q->sysfs_lock);
 		return -ENOENT;
 	}