mpc512x_dma: remove useless use of lock

mpc_dma_tx_status(struct dma_chan *chan, dma_cookie_t cookie,

	       struct dma_tx_state *txstate)

{

	struct mpc_dma_chan *mchan = dma_chan_to_mpc_dma_chan(chan);

	enum dma_status ret;

	unsigned long flags;

	spin_lock_irqsave(&mchan->lock, flags);

	ret = dma_cookie_status(chan, cookie, txstate);

	spin_unlock_irqrestore(&mchan->lock, flags);

	return ret;

	return dma_cookie_status(chan, cookie, txstate);

}

/* Prepare descriptor for memory to memory copy */