blk-iolatency: fix blkg leak in timer_fn

At this point we have a ref on the blkg, we need to drop it if we don't
have a iolat.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-iolatency.c

@@ -627,7 +627,7 @@ static void blkiolatency_timer_fn(struct timer_list *t)
 
 		iolat = blkg_to_lat(blkg);
 		if (!iolat)
-			continue;
+			goto next;
 
 		lat_info = &iolat->child_lat;
 		cookie = atomic_read(&lat_info->scale_cookie);