serial: stm32: use the defined variable to simplify code

Use the defined variable 'dev' to make the code cleaner.
Signed-off-by: Zhang Shengju <zhangshengju@cmss.chinamobile.com>
Signed-off-by: Tang Bin <tangbin@cmss.chinamobile.com>
Link: https://lore.kernel.org/r/20210814124951.30084-1-tangbin@cmss.chinamobile.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/stm32-usart.c

@@ -1177,7 +1177,7 @@ static int stm32_usart_of_dma_rx_probe(struct stm32_port *stm32port,
 	if (uart_console(port))
 		return -ENODEV;
 
-	stm32port->rx_buf = dma_alloc_coherent(&pdev->dev, RX_BUF_L,
+	stm32port->rx_buf = dma_alloc_coherent(dev, RX_BUF_L,
 					       &stm32port->rx_dma_buf,
 					       GFP_KERNEL);
 	if (!stm32port->rx_buf)
@@ -1243,7 +1243,7 @@ static int stm32_usart_of_dma_tx_probe(struct stm32_port *stm32port,
 
 	stm32port->tx_dma_busy = false;
 
-	stm32port->tx_buf = dma_alloc_coherent(&pdev->dev, TX_BUF_L,
+	stm32port->tx_buf = dma_alloc_coherent(dev, TX_BUF_L,
 					       &stm32port->tx_dma_buf,
 					       GFP_KERNEL);
 	if (!stm32port->tx_buf)