btrfs: hide test-only member under ifdef

Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -1181,8 +1181,10 @@ struct btrfs_root {
 
 	u64 highest_objectid;
 
+#ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
 	/* only used with CONFIG_BTRFS_FS_RUN_SANITY_TESTS is enabled */
 	u64 alloc_bytenr;
+#endif
 
 	u64 defrag_trans_start;
 	struct btrfs_key defrag_progress;

fs/btrfs/extent-tree.c

@@ -8354,6 +8354,7 @@ struct extent_buffer *btrfs_alloc_tree_block(struct btrfs_trans_handle *trans,
 	bool skinny_metadata = btrfs_fs_incompat(root->fs_info,
 						 SKINNY_METADATA);
 
+#ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
 	if (btrfs_test_is_dummy_root(root)) {
 		buf = btrfs_init_new_buffer(trans, root, root->alloc_bytenr,
 					    level);
@@ -8361,6 +8362,7 @@ struct extent_buffer *btrfs_alloc_tree_block(struct btrfs_trans_handle *trans,
 			root->alloc_bytenr += blocksize;
 		return buf;
 	}
+#endif
 
 	block_rsv = use_block_rsv(trans, root, blocksize);
 	if (IS_ERR(block_rsv))