vp_vdpa: correct the return value when fail to map notification

We forget to assign a error value when we fail to map the notification
during prove. This patch fixes it.

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: 11d8ffed00 ("vp_vdpa: switch to use vp_modern_map_vq_notify()")
Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20210624035939.26618-1-jasowang@redhat.com
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/vdpa/virtio_pci/vp_vdpa.c

@@ -442,6 +442,7 @@ static int vp_vdpa_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 			vp_modern_map_vq_notify(mdev, i,
 						&vp_vdpa->vring[i].notify_pa);
 		if (!vp_vdpa->vring[i].notify) {
+			ret = -EINVAL;
 			dev_warn(&pdev->dev, "Fail to map vq notify %d\n", i);
 			goto err;
 		}