s390x/pci: Always delete and free the release_timer

s390x/pci: Always delete and free the release_timer

We should always get rid of it. I don't see a reason to keep the timer
alive if the devices are going away. This looks like a memory leak.

(hmp) device_add virtio-mouse-pci,id=test
(hmp) device_del test
-> guest notified, timer pending.
-> guest does not react for some reason (e.g. crash)
-> s390_pcihost_timer_cb(). Timer not pending anymore. qmp_unplug().

-> Device deleted. Timer expired (not pending) but not freed.

Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20190114103110.10909-4-david@redhat.com>
Reviewed-by: Collin Walling <walling@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>