hw/virtio/vhost-vdpa: Fix Coverity CID 1432864

Fix uninitialized value issues reported by Coverity:

  Field 'msg.reserved' is uninitialized when calling write().

Fixes: a5bd0580 ("vhost-vdpa: batch updating IOTLB mappings")
Reported-by: Coverity (CID 1432864: UNINIT)
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20201028154004.776760-1-philmd@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/virtio/vhost-vdpa.c

@@ -90,7 +90,7 @@ static void vhost_vdpa_listener_begin(MemoryListener *listener)
 {
     struct vhost_vdpa *v = container_of(listener, struct vhost_vdpa, listener);
     struct vhost_dev *dev = v->dev;
-    struct vhost_msg_v2 msg;
+    struct vhost_msg_v2 msg = {};
     int fd = v->device_fd;
 
     if (!(dev->backend_cap & (0x1ULL << VHOST_BACKEND_F_IOTLB_BATCH))) {
@@ -110,7 +110,7 @@ static void vhost_vdpa_listener_commit(MemoryListener *listener)
 {
     struct vhost_vdpa *v = container_of(listener, struct vhost_vdpa, listener);
     struct vhost_dev *dev = v->dev;
-    struct vhost_msg_v2 msg;
+    struct vhost_msg_v2 msg = {};
     int fd = v->device_fd;
 
     if (!(dev->backend_cap & (0x1ULL << VHOST_BACKEND_F_IOTLB_BATCH))) {