drm/amdgpu: fix placement flags in amdgpu_ttm_bind

Otherwise we lose the NO_EVICT flag and can try to evict pinned BOs.

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