serial: 8250: lock port for stop_rx() in omap8250_irq()

The uarts_ops stop_rx() callback expects that the port->lock is
taken and interrupts are disabled.

Fixes: 1fe0e1fa ("serial: 8250_omap: Handle optional overrun-throttle-ms property")
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Tony Lindgren <tony@atomide.com>
Link: https://lore.kernel.org/r/20230525093159.223817-4-john.ogness@linutronix.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_omap.c

@@ -658,7 +658,9 @@ static irqreturn_t omap8250_irq(int irq, void *dev_id)
 
 		up->ier = port->serial_in(port, UART_IER);
 		if (up->ier & (UART_IER_RLSI | UART_IER_RDI)) {
+			spin_lock(&port->lock);
 			port->ops->stop_rx(port);
+			spin_unlock(&port->lock);
 		} else {
 			/* Keep restarting the timer until
 			 * the input overrun subsides.