drm/nouveau: fix notifier memory corruption bug

nouveau_bo_wr32 expects offset to be in words, but we pass value in bytes,
so after commit 73412c38 ("drm/nouveau: allocate
kernel's notifier object at end of block") we started to overwrite some memory
after notifier buffer object (previously m2mf_ntfy was always 0, so it didn't
matter it was a value in bytes).
Reported-by: Dominik Brodowski <linux@dominikbrodowski.net>
Reported-by: Nigel Cunningham <lkml@nigelcunningham.com.au>
Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Pekka Paalanen <pq@iki.fi>
Cc: stable@kernel.org    [2.6.38]
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_fbcon.c

@@ -181,13 +181,13 @@ nouveau_fbcon_sync(struct fb_info *info)
 		OUT_RING  (chan, 0);
 	}
 
-	nouveau_bo_wr32(chan->notifier_bo, chan->m2mf_ntfy + 3, 0xffffffff);
+	nouveau_bo_wr32(chan->notifier_bo, chan->m2mf_ntfy/4 + 3, 0xffffffff);
 	FIRE_RING(chan);
 	mutex_unlock(&chan->mutex);
 
 	ret = -EBUSY;
 	for (i = 0; i < 100000; i++) {
-		if (!nouveau_bo_rd32(chan->notifier_bo, chan->m2mf_ntfy + 3)) {
+		if (!nouveau_bo_rd32(chan->notifier_bo, chan->m2mf_ntfy/4 + 3)) {
 			ret = 0;
 			break;
 		}