tty: 8250: Fix port count of PX-257

The port count of the PX-257 Rev3 is actually 2, not 4.

Fixes: ef5a03a ("tty: 8250: Add support for Brainboxes PX cards.")
Cc: stable@vger.kernel.org
Signed-off-by: Cameron Williams <cang1@live.co.uk>
Link: https://lore.kernel.org/r/DU0PR02MB7899C804D9F04E727B5A0E8FC4DBA@DU0PR02MB7899.eurprd02.prod.outlook.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Cameron Williams

drivers/tty/serial/8250/8250_pci.c

@@ -5230,7 +5230,7 @@ static const struct pci_device_id serial_pci_tbl[] = {
 	{	PCI_VENDOR_ID_INTASHIELD, 0x4015,
 		PCI_ANY_ID, PCI_ANY_ID,
 		0, 0,
-		pbn_oxsemi_4_15625000 },
+		pbn_oxsemi_2_15625000 },
 	/*
 	 * Brainboxes PX-260/PX-701
 	 */