We will record the fs root or the reloc root in the trans in
select_reloc_root.  These will actually return errors in the following
patches, so check their return value here and return it up the stack.
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>