Fix local_item_size error on some GPUs
Fix local_item_size error on some GPUs

funguito/Sia-GPU-Miner,NebulousLabs/Sia-GPU-Miner,funguito/Sia-GPU-Miner,visvirial/Sia-GPU-Miner,visvirial/Sia-GPU-Miner,NebulousLabs/Sia-GPU-Miner