conf: fix parsing 'cmd_per_lun' and 'max_sectors'

commit d9504941 introduces two new attributes "cmd_per_lun" and
"max_sectors" same with the names QEMU uses for virtio-scsi.
But the case of parsing them is not exact. Change to parse
them if controller has "driver" element.
Signed-off-by: NMo yuxiang <moyuxiang@huawei.com>
(cherry picked from commit ca8ef1df)

src/conf/domain_conf.c

@@ -6188,10 +6188,11 @@ virDomainControllerDefParseXML(xmlNodePtr node,
     cur = node->children;
     while (cur != NULL) {
         if (cur->type == XML_ELEMENT_NODE) {
-            if (xmlStrEqual(cur->name, BAD_CAST "driver"))
+            if (xmlStrEqual(cur->name, BAD_CAST "driver")) {
                 queues = virXMLPropString(cur, "queues");
                 cmd_per_lun = virXMLPropString(cur, "cmd_per_lun");
                 max_sectors = virXMLPropString(cur, "max_sectors");
+            }
         }
         cur = cur->next;
     }