We're supposed to print the root_key.offset in btrfs_root_name in the
case of a reloc root, not the objectid.  Fix this helper to take the key
so we have access to the offset when we need it.

Fixes: 457f1864 ("btrfs: pretty print leaked root name")
Reviewed-by: NQu Wenruo <wqu@suse.com>
Reviewed-by: NNikolay Borisov <nborisov@suse.com>
Signed-off-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>