SiS DRM: fix a pointer cast warning

Fix a pointer cast warning in the SIS DRM code.

This was introduced in patch ce65a44de07f73ceda1749812b75086b7add408d.

Signed-off-by: David Howells <[e-mail]>
Cc: Dave Airlie <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Dave Airlie <[e-mail]>

drivers/gpu/drm/sis/sis_mm.c

···
 	if (req.size == 0)
 		return NULL;
 	else
-		return (void *)~req.offset;
+		return (void *)(unsigned long)~req.offset;
 }
 
 static void sis_sman_mm_free(void *private, void *ref)