serial: 8250_pxa: honor the port number from devicetree

Like the other OF-enabled drivers, use the port number from the firmware if
the devicetree specifies an alias:

aliases {
...
serial2 = &uart2; /* Should be ttyS2 */
}

This is how the deprecated pxa.c driver behaved, switching to 8250_pxa
messes up the numbering.

Signed-off-by: Lubomir Rintel <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/8250/8250_pxa.c

···
 	if (ret)
 		return ret;
 
+	ret = of_alias_get_id(pdev->dev.of_node, "serial");
+	if (ret >= 0)
+		uart.port.line = ret;
+
 	uart.port.type = PORT_XSCALE;
 	uart.port.iotype = UPIO_MEM32;
 	uart.port.mapbase = mmres->start;