drm/ttm: cleanup ttm_tt_(unbind|destroy)

ttm_tt_destroy should be the only one unbinding the object.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
4 files changed