mon: fix mon scaledown when mons are portable

in case of portable mons, mon scaledown was skipped
with below code
```
if mon.NodeName == "" {
			logger.Debugf("mon %q is not scheduled to a specific host", mon.DaemonName)
			continue
		}
```
which skips mon removal if mon nodeName is empty
but if mons are scale down in case of portable mons
in that case also we want to remove extra mons to match
the cephCluster configuration.

Signed-off-by: subhamkrai <srai@redhat.com>
(cherry picked from commit d23a8433ed)

pkg/operator/ceph/cluster/mon/health.go

@@ -450,6 +450,7 @@ func (c *Cluster) determineExtraMonToRemove() string {
 	for _, mon := range mons {
 		if mon.NodeName == "" {
 			logger.Debugf("mon %q is not scheduled to a specific host", mon.DaemonName)
+			arbitraryMon = mon.DaemonName
 			continue
 		}
 		// Check if there are multiple mons on the node