btrfs: tree-checker: Fix misleading group system information

commit 761333f2f50ccc887aa9957ae829300262c0d15b upstream.

block_group_err shows the group system as a decimal value with a '0x'
prefix, which is somewhat misleading.

Fix it to print hexadecimal, as was intended.

Fixes: fce466eab7ac6 ("btrfs: tree-checker: Verify block_group_item")
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Shaokun Zhang <zhangshaokun@hisilicon.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>