drm/amdgpu: initialize the vmid_wait with the stub fence

This way we don't need to check for NULL any more.
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -204,7 +204,7 @@ static int amdgpu_vmid_grab_idle(struct amdgpu_vm *vm,
 	unsigned i;
 	int r;
 
-	if (ring->vmid_wait && !dma_fence_is_signaled(ring->vmid_wait))
+	if (!dma_fence_is_signaled(ring->vmid_wait))
 		return amdgpu_sync_fence(sync, ring->vmid_wait);
 
 	fences = kmalloc_array(id_mgr->num_ids, sizeof(void *), GFP_KERNEL);

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

@@ -193,6 +193,7 @@ int amdgpu_ring_init(struct amdgpu_device *adev, struct amdgpu_ring *ring,
 		adev->rings[ring->idx] = ring;
 		ring->num_hw_submission = sched_hw_submission;
 		ring->sched_score = sched_score;
+		ring->vmid_wait = dma_fence_get_stub();
 		r = amdgpu_fence_driver_init_ring(ring);
 		if (r)
 			return r;