drm/nouveau: Skip vga_fini on non-PCI device

As with vga_init, this function doesn't make sense on non-PCI devices,
and the Thunderbolt check in it dereferences a NULL pointer in that
case. Add some code to skip this function when the device is not a PCI
device.
Signed-off-by: NMikko Perttunen <mperttunen@nvidia.com>
Signed-off-by: NBen Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_vga.c

@@ -111,6 +111,10 @@ nouveau_vga_fini(struct nouveau_drm *drm)
 	struct drm_device *dev = drm->dev;
 	bool runtime = nouveau_pmops_runtime();
 
+	/* only relevant for PCI devices */
+	if (!dev->pdev)
+		return;
+
 	vga_client_register(dev->pdev, NULL, NULL, NULL);
 
 	if (pci_is_thunderbolt_attached(dev->pdev))