ublk: mention WRITE_ZEROES in comment of ublk_complete_rq()

WRITE_ZEROES won't return bytes returned just like FLUSH and DISCARD,
and we can end it directly. Add missing comment for it in
ublk_complete_rq().
Signed-off-by: Ziyang Zhang <ZiyangZhang@linux.alibaba.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20230207070839.370817-3-ZiyangZhang@linux.alibaba.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/ublk_drv.c

@@ -665,7 +665,7 @@ static void ublk_complete_rq(struct request *req)
 	}
 
 	/*
-	 * FLUSH or DISCARD usually won't return bytes returned, so end them
+	 * FLUSH, DISCARD or WRITE_ZEROES usually won't return bytes returned, so end them
 	 * directly.
 	 *
 	 * Both the two needn't unmap.