Apart from some code inside ttm itself and nouveau_bo_vma_del,
this is the only place where ttm_bo_wait is used without a reservation.
Fix this so we can remove the fence_lock later on.

After the switch to rcu the reservation lock will be
removed again.
Signed-off-by: NMaarten Lankhorst <maarten.lankhorst@canonical.com>
Acked-by: NBen Skeggs <bskeggs@redhat.com>