Fixes a use-after-free due to a race condition in
ttm_bo_cleanup_refs_and_unlock, which allows one task to reserve a BO
and destroy its ttm_resv while another task is waiting for it to signal
in reservation_object_wait_timeout_rcu.

v2:
* Always initialize bo->ttm_resv in ttm_bo_init_reserved
 (Christian König)

Fixes: 0d2bd2ae "drm/ttm: fix memory leak while individualizing BOs"
Reviewed-by: Chunming Zhou <david1.zhou@amd.com> # v1
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>