SiS DRM: fix a pointer cast warning

Fix a pointer cast warning in the SIS DRM code.

This was introduced in patch ce65a44de0.

Signed-off-by: David Howells <dhowells@redhat.com>
Cc: Dave Airlie <airlied@linux.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/sis/sis_mm.c

@@ -57,7 +57,7 @@ static void *sis_sman_mm_allocate(void *private, unsigned long size,
 	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)