rgw: fix `bi put` not using right bucket index shard

rgw: fix `bi put` not using right bucket index shard

When `radosgw-admin bi put` adds an entry for an incomplete multipart
upload, the bucket index shard is not calculated correctly. It should
be based on the name of the ultimate object. However the calculation
was including the added organizational suffixes as well. This corrects
that.

NOTE: When entries are not put in the correct index shard, unordered
listing becomes unreliable, perhaps causing entries to be skipped or
infinite loops to form.

Signed-off-by: J. Eric Ivancich <ivancich@redhat.com>