btrfs: simplify gotos in open_seed_device

The function does not have a common exit block and returns immediatelly
so there's no point having the goto. Remove the two cases.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>