Initialization error of controller in QEmu SCSI hotplug

Bug manifests itself by:

1. # virsh attach-disk --target sdb ...
2. # virsh attach-disk --target sdh ...
   error: Failed to attach disk
   error: operation failed: target scsi:0 already exists

sdh uses scsi:1, rather than scsi:0.

* src/qemu/qemu_hotplug.c: properly set controller idx in
  qemuDomainFindOrCreateSCSIDiskController()

src/qemu/qemu_hotplug.c

@@ -321,7 +321,7 @@ qemuDomainFindOrCreateSCSIDiskController(struct qemud_driver *driver,
         return NULL;
     }
     cont->type = VIR_DOMAIN_CONTROLLER_TYPE_SCSI;
-    cont->idx = 0;
+    cont->idx = controller;
     cont->model = -1;
 
     VIR_INFO0("No SCSI controller present, hotplugging one");