drm/amdkfd: fix ttm size refactor fallout

drm/amdkfd: fix ttm size refactor fallout

I guess Christian didn't compile test amdkfd.

Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Fixes: 731331d9d025 ("drm/ttm: cleanup BO size handling v3")
Cc: Christian König <christian.koenig@amd.com>
Cc: Huang Rui <ray.huang@amd.com> (v1)
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Felix Kuehling <Felix.Kuehling@amd.com>
Cc: amd-gfx@lists.freedesktop.org
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201214191725.3899147-1-daniel.vetter@ffwll.ch