ReplicatedPG::maybe_handle_cache: do not skip promote for write_ordered

We cannot redirect a RW ordered read.

Fixes: #9064
Introduced: 0ed3adc1e0a74bf9548d1d956aece11f019afee0
Signed-off-by: Samuel Just <sam.just@inktank.com>
Merge pull request #2246 from ceph/wip-9064

ReplicatedPG::maybe_handle_cache: do not skip promote for write_ordered

Reviewed-by: Sage Weil <sage@redhat.com>