qemu: syntax fix

Pushed without ack, under the trivial rule.
(cherry picked from commit 2beed2da)

src/qemu/qemu_hotplug.c

@@ -1170,7 +1170,7 @@ int qemuDomainAttachHostDevice(struct qemud_driver *driver,
 
         if (usbDeviceListAdd(list, usb) < 0) {
             usbFreeDevice(usb);
-            usb = NULL:
+            usb = NULL;
             goto cleanup;
         }