cluster/olm/ceph/README.md: fix inconsistent references to Makefile target
cluster/olm/ceph/README.md: fix inconsistent references to Makefile target

0fc3775b990d0c79356be33f8fc8416a897560fc added csv-ceph target to Makefile,
but README.md refers to non-existent 'csv' target. This comment aligns
it.

Signed-off-by: Mateusz Gozdek <13f764135ff35d07236cdb9e39f2edb4395b2583@gmail.com>

rook/rook,rook/nfs,rook/rook,rook/rook,rook/nfs,rook/rook,rook/nfs,rook/rook