btrfs: don't use the extent root in btrfs_chunk_alloc_add_chunk_item

We're just using the extent_root to set the chunk owner to
root_key->objectid, which is BTRFS_EXTENT_TREE_OBJECTID, so use that
directly instead of using the root.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/volumes.c

@@ -5541,7 +5541,6 @@ int btrfs_chunk_alloc_add_chunk_item(struct btrfs_trans_handle *trans,
 				     struct btrfs_block_group *bg)
 {
 	struct btrfs_fs_info *fs_info = trans->fs_info;
-	struct btrfs_root *extent_root = fs_info->extent_root;
 	struct btrfs_root *chunk_root = fs_info->chunk_root;
 	struct btrfs_key key;
 	struct btrfs_chunk *chunk;
@@ -5613,7 +5612,7 @@ int btrfs_chunk_alloc_add_chunk_item(struct btrfs_trans_handle *trans,
 	}
 
 	btrfs_set_stack_chunk_length(chunk, bg->length);
-	btrfs_set_stack_chunk_owner(chunk, extent_root->root_key.objectid);
+	btrfs_set_stack_chunk_owner(chunk, BTRFS_EXTENT_TREE_OBJECTID);
 	btrfs_set_stack_chunk_stripe_len(chunk, map->stripe_len);
 	btrfs_set_stack_chunk_type(chunk, map->type);
 	btrfs_set_stack_chunk_num_stripes(chunk, map->num_stripes);