virtio/virtio_pci_legacy_dev: ensure the correct return value

When pci_iomap return NULL, the return value is zero.
Signed-off-by: Peng Hao <flyingpeng@tencent.com>
Link: https://lore.kernel.org/r/20211222112014.87394-1-flyingpeng@tencent.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>

drivers/virtio/virtio_pci_legacy_dev.c

@@ -45,8 +45,10 @@ int vp_legacy_probe(struct virtio_pci_legacy_device *ldev)
 		return rc;
 
 	ldev->ioaddr = pci_iomap(pci_dev, 0, 0);
-	if (!ldev->ioaddr)
+	if (!ldev->ioaddr) {
+		rc = -EIO;
 		goto err_iomap;
+	}
 
 	ldev->isr = ldev->ioaddr + VIRTIO_PCI_ISR;