drm/amdkfd: Add NULL-pointer check

top_dev->gpu is NULL for CPUs. Avoid dereferencing it if NULL.

Acked-by: Alex Deucher <[e-mail]>
Signed-off-by: Felix Kuehling <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/amdkfd/kfd_topology.c

···
 	down_read(&topology_lock);
 
 	list_for_each_entry(top_dev, &topology_device_list, list)
-		if (top_dev->gpu->pdev == pdev) {
+		if (top_dev->gpu && top_dev->gpu->pdev == pdev) {
 			device = top_dev->gpu;
 			break;
 		}