tty: serial/bcm63xx_uart: fix sparse warning

this patch fixes following sparse warnings:

bcm63xx_uart.c:857:43: warning: Using plain integer as NULL pointer
bcm63xx_uart.c:871:35: warning: Using plain integer as NULL pointer
Signed-off-by: NLad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/bcm63xx_uart.c

@@ -854,7 +854,7 @@ static int bcm_uart_probe(struct platform_device *pdev)
 
 	ret = uart_add_one_port(&bcm_uart_driver, port);
 	if (ret) {
-		ports[pdev->id].membase = 0;
+		ports[pdev->id].membase = NULL;
 		return ret;
 	}
 	platform_set_drvdata(pdev, port);
@@ -868,7 +868,7 @@ static int bcm_uart_remove(struct platform_device *pdev)
 	port = platform_get_drvdata(pdev);
 	uart_remove_one_port(&bcm_uart_driver, port);
 	/* mark port as free */
-	ports[pdev->id].membase = 0;
+	ports[pdev->id].membase = NULL;
 	return 0;
 }