btrfs: tree-checker: Replace root parameter with fs_info

When inspecting the error message with real corruption, the "root=%llu"
always shows "1" (root tree), instead of the correct owner.

The problem is that we are getting @root from page->mapping->host, which
points the same btree inode, so we will always get the same root.

This makes the root owner output meaningless, and harder to port
tree-checker to btrfs-progs.

So get rid of the false and meaningless @root parameter and replace it
with @fs_info.
To get the owner, we can only rely on btrfs_header_owner() now.

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