serial: 8250_dw: Use serial_lsr_in() in dw8250_handle_irq()

dw8250_handle_irq() reads LSR under a few conditions, convert both to
use serial_lsr_in() in order to preserve LSR flags properly across
reads.

Fixes: 424d7918 ("serial: 8250_dw: Avoid "too much work" from bogus rx timeout interrupt")
Fixes: aa63d786 ("serial: 8250: dw: Add support for DMA flow controlling devices")
Cc: Douglas Anderson <dianders@chromium.org>
Cc: Phil Edworthy <phil.edworthy@renesas.com>
Cc: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20220608095431.18376-6-ilpo.jarvinen@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_dw.c

@@ -253,7 +253,7 @@ static int dw8250_handle_irq(struct uart_port *p)
 	 */
 	if (!up->dma && rx_timeout) {
 		spin_lock_irqsave(&p->lock, flags);
-		status = p->serial_in(p, UART_LSR);
+		status = serial_lsr_in(up);
 
 		if (!(status & (UART_LSR_DR | UART_LSR_BI)))
 			(void) p->serial_in(p, UART_RX);
@@ -263,7 +263,7 @@ static int dw8250_handle_irq(struct uart_port *p)
 
 	/* Manually stop the Rx DMA transfer when acting as flow controller */
 	if (quirks & DW_UART_QUIRK_IS_DMA_FC && up->dma && up->dma->rx_running && rx_timeout) {
-		status = p->serial_in(p, UART_LSR);
+		status = serial_lsr_in(up);
 		if (status & (UART_LSR_DR | UART_LSR_BI)) {
 			dw8250_writel_ext(p, RZN1_UART_RDMACR, 0);
 			dw8250_writel_ext(p, DW_UART_DMASA, 1);