Typo on DISTRIBUTED_STORAGE_PREFERENCE in quay documentation

The DISTRIBUTED_STORAGE_PREFERENCE value in the documentation below needs to match the added storage engine in our docs. 

    Chapter 3. Configuring Quay before deployment Red Hat Quay 3 | Red Hat Customer Portal
    URL:   https://access.redhat.com/documentation/en-us/red_hat_quay/3/html/deploy_red_hat_quay_on_openshift_with_the_quay_operator/operator-preconfigure#ceph_radosgw_storage_hitachi_hcp_storage

Recently an internal team ran into some problems with quay and came across this value which without an understanding of the product is not obvious. Fixing this to match the attached storage engine would resolve that inconsistency.

Thanks