vhost/vsock: fix uninitialized vhost_vsock->guest_cid

The vhost_vsock->guest_cid field is uninitialized when /dev/vhost-vsock
is opened until the VHOST_VSOCK_SET_GUEST_CID ioctl is called.

kvmalloc(..., GFP_KERNEL | __GFP_RETRY_MAYFAIL) does not zero memory.
All other vhost_vsock fields are initialized explicitly so just
initialize this field too.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/vhost/vsock.c

@@ -518,6 +518,8 @@ static int vhost_vsock_dev_open(struct inode *inode, struct file *file)
 		goto out;
 	}
 
+	vsock->guest_cid = 0; /* no CID assigned yet */
+
 	atomic_set(&vsock->queued_replies, 0);
 
 	vqs[VSOCK_VQ_TX] = &vsock->vqs[VSOCK_VQ_TX];