cls_rgw: fix object name of objects removed on object creation

Fixes: #8972
Backport: firefly, dumpling

Reported-by: Patrycja Szabłowska <szablowska.patrycja@gmail.com>
Signed-off-by: Yehuda Sadeh <yehuda@redhat.com>
Merge pull request #2168 from ceph/wip-8972

cls_rgw: fix object name of objects removed on object creation

Reviewed-by: Josh Durgin <josh.durgin@inktank.com>