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: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/serial/bcm63xx_uart.c b/drivers/tty/serial/bcm63xx_uart.c
index 01d83df..681e0f3 100644
--- a/drivers/tty/serial/bcm63xx_uart.c
+++ b/drivers/tty/serial/bcm63xx_uart.c
@@ -854,7 +854,7 @@
 
 	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 @@
 	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;
 }