drm/ttm: use ttm put pages function to properly restore cache attribute

On failure we need to make sure the page we free has wb cache
attribute. Do this pas call the proper ttm page helper function.

Signed-off-by: Jerome Glisse <jglisse@redhat.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>