Btrfs: don't warn in btrfs_add_orphan

When I moved the orphan adding to btrfs_truncate I missed the fact that during
orphan cleanup we just add the orphan items to the orphan list without going
through btrfs_orphan_add, which results in lots of warnings on mount if you have
any orphan items that need to be truncated.  Just remove this warning since it's
ok, this will allow all of the normal space accounting take place.  Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>