drm/ttm: remove NULL checks when calling ttm_tt_destroy

The function is a no-op with a NULL pointer.

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>
3 files changed