btrfs: switch extent_io_tree::track_uptodate to bool

This patch is split from the following one "btrfs: Introduce
extent_io_tree::owner to distinguish different io_trees" from Qu, so the
different changes are not mixed together.

Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index e63215d6..bd5c125 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -111,7 +111,7 @@ struct extent_io_tree {
 	struct btrfs_fs_info *fs_info;
 	void *private_data;
 	u64 dirty_bytes;
-	int track_uptodate;
+	bool track_uptodate;
 	spinlock_t lock;
 	const struct extent_io_ops *ops;
 };