drm/amd/amdgpu: add error handling to amdgpu_virt_read_pf2vf_data

[Why]
when vram lost happened in guest, try to write vram can lead to
kernel stuck.

[How]
When the readback data is invalid, don't do write work, directly
reschedule a new work.
Signed-off-by: Jingwen Chen <Jingwen.Chen2@amd.com>
Reviewed-by: Monk Liu<monk.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -560,10 +560,14 @@ static int amdgpu_virt_write_vf2pf_data(struct amdgpu_device *adev)
 static void amdgpu_virt_update_vf2pf_work_item(struct work_struct *work)
 {
 	struct amdgpu_device *adev = container_of(work, struct amdgpu_device, virt.vf2pf_work.work);
+	int ret;
 
-	amdgpu_virt_read_pf2vf_data(adev);
+	ret = amdgpu_virt_read_pf2vf_data(adev);
+	if (ret)
+		goto out;
 	amdgpu_virt_write_vf2pf_data(adev);
 
+out:
 	schedule_delayed_work(&(adev->virt.vf2pf_work), adev->virt.vf2pf_update_interval_ms);
 }