vbox: Fix build after xenbus addition

Commit 09eb1ae0 added a new enum type for xenbus, and adjusted
affected switch statements in the qemu driver, but failed to notice
that the vbox driver had a similar switch statement.
Signed-off-by: NEric Blake <eblake@redhat.com>

src/vbox/vbox_common.c

@@ -377,6 +377,7 @@ vboxSetStorageController(virDomainControllerDefPtr controller,
     case VIR_DOMAIN_CONTROLLER_TYPE_CCID:
     case VIR_DOMAIN_CONTROLLER_TYPE_USB:
     case VIR_DOMAIN_CONTROLLER_TYPE_PCI:
+    case VIR_DOMAIN_CONTROLLER_TYPE_XENBUS:
     case VIR_DOMAIN_CONTROLLER_TYPE_LAST:
         virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
                        _("The vbox driver does not support %s controller type"),