qemu: process: Fix alias for disk-tray-moved event

Currently we'd report the alias of the drive which is backing the cdrom
rather than the device itself:

 $ virsh event ds tray-change --loop
 event 'tray-change' for domain ds disk drive-ide0-0-1: opened
 event 'tray-change' for domain ds disk drive-ide0-0-1: closed

Report the disk device alias as we document in the API docs:

https://libvirt.org/html/libvirt-libvirt-domain.html#virConnectDomainEventTrayChangeCallbackSigned-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

src/qemu/qemu_process.c

@@ -1053,9 +1053,7 @@ qemuProcessHandleTrayChange(qemuMonitorPtr mon ATTRIBUTE_UNUSED,
     disk = qemuProcessFindDomainDiskByAlias(vm, devAlias);
 
     if (disk) {
-        event = virDomainEventTrayChangeNewFromObj(vm,
-                                                   devAlias,
-                                                   reason);
+        event = virDomainEventTrayChangeNewFromObj(vm, disk->info.alias, reason);
         /* Update disk tray status */
         if (reason == VIR_DOMAIN_EVENT_TRAY_CHANGE_OPEN)
             disk->tray_status = VIR_DOMAIN_DISK_TRAY_OPEN;