drm/amd/amdgpu: handle return value of amdgpu_driver_load_kms

if guest driver failed to enter full GPU access, amdgpu_driver_load_kms
will unload kms and free dev->dev_private, drm_dev_register would access
null pointer. Driver will enter an error state and can't be unloaded.
Signed-off-by: Liu ChengZhe <ChengZhe.Liu@amd.com>
Reviewed-by: Madhav Chauhan <madhav.chauhan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c

@@ -1111,7 +1111,9 @@ static int amdgpu_pci_probe(struct pci_dev *pdev,
 
 	pci_set_drvdata(pdev, dev);
 
-	amdgpu_driver_load_kms(dev, ent->driver_data);
+	ret = amdgpu_driver_load_kms(dev, ent->driver_data);
+	if (ret)
+		goto err_pci;
 
 retry_init:
 	ret = drm_dev_register(dev, ent->driver_data);