serial: pch_uart: Pass correct sg to dma_unmap_sg()

A local variable sg is used to store scatterlist pointer in
pch_dma_tx_complete(). The for loop doing Tx byte accounting before
dma_unmap_sg() alters sg in its increment statement. Therefore, the
pointer passed into dma_unmap_sg() won't match to the one given to
dma_map_sg().

To fix the problem, use priv->sg_tx_p directly in dma_unmap_sg()
instead of the local variable.

Fixes: da3564ee ("pch_uart: add multi-scatter processing")
Cc: stable@vger.kernel.org
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20230103093435.4396-1-ilpo.jarvinen@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/pch_uart.c

@@ -749,7 +749,7 @@ static void pch_dma_tx_complete(void *arg)
 		uart_xmit_advance(port, sg_dma_len(sg));
 
 	async_tx_ack(priv->desc_tx);
-	dma_unmap_sg(port->dev, sg, priv->orig_nent, DMA_TO_DEVICE);
+	dma_unmap_sg(port->dev, priv->sg_tx_p, priv->orig_nent, DMA_TO_DEVICE);
 	priv->tx_dma_use = 0;
 	priv->nent = 0;
 	priv->orig_nent = 0;