btrfs: Replace fs_info->cache_workers workqueue with btrfs_workqueue.

Replace the fs_info->cache_workers with the newly created
btrfs_workqueue.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Tested-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Josef Bacik <jbacik@fb.com>
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 32312e0..bb58082 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -378,7 +378,7 @@
 	return total_added;
 }
 
-static noinline void caching_thread(struct btrfs_work *work)
+static noinline void caching_thread(struct btrfs_work_struct *work)
 {
 	struct btrfs_block_group_cache *block_group;
 	struct btrfs_fs_info *fs_info;
@@ -549,7 +549,7 @@
 	caching_ctl->block_group = cache;
 	caching_ctl->progress = cache->key.objectid;
 	atomic_set(&caching_ctl->count, 1);
-	caching_ctl->work.func = caching_thread;
+	btrfs_init_work(&caching_ctl->work, caching_thread, NULL, NULL);
 
 	spin_lock(&cache->lock);
 	/*
@@ -640,7 +640,7 @@
 
 	btrfs_get_block_group(cache);
 
-	btrfs_queue_worker(&fs_info->caching_workers, &caching_ctl->work);
+	btrfs_queue_work(fs_info->caching_workers, &caching_ctl->work);
 
 	return ret;
 }