spi-topcliff-pch: add tx-memory clear after complete transmitting

Currently, in case of reading date from SPI flash,
command is sent twice.
The cause is that tx-memory clear processing is missing .
This patch adds the tx-momory clear processing.
Signed-off-by: NTomoya MORINAGA <tomoya-linux@dsn.okisemi.com>
Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>

drivers/spi/spi-topcliff-pch.c

@@ -837,6 +837,11 @@ static void pch_spi_start_transfer(struct pch_spi_data *data)
 
 	dma_sync_sg_for_cpu(&data->master->dev, dma->sg_rx_p, dma->nent,
 			    DMA_FROM_DEVICE);
+
+	dma_sync_sg_for_cpu(&data->master->dev, dma->sg_tx_p, dma->nent,
+			    DMA_FROM_DEVICE);
+	memset(data->dma.tx_buf_virt, 0, PAGE_SIZE);
+
 	async_tx_ack(dma->desc_rx);
 	async_tx_ack(dma->desc_tx);
 	kfree(dma->sg_tx_p);