It's not used by any driver. The destructor callback is unfortunately
used by the via driver in a rather convoluted piece of code used
to reimplement something resembling broken futexes. I didn't dare
to touch this code. But at least kill the needless NULL assignemt
in the sis driver.
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: NDave Airlie <airlied@redhat.com>