altera_uart: Don't use plain integer as NULL pointer

Fixes sparse warning.
Signed-off-by: NAnton Vorontsov <cbouatmailru@gmail.com>
Cc: Alan Cox <alan@linux.intel.com>
Acked-by: NTobias Klauser <tklauser@distanz.ch>

drivers/serial/altera_uart.c

@@ -461,7 +461,7 @@ static int __init altera_uart_console_setup(struct console *co, char *options)
 	if (co->index < 0 || co->index >= CONFIG_SERIAL_ALTERA_UART_MAXPORTS)
 		return -EINVAL;
 	port = &altera_uart_ports[co->index].port;
-	if (port->membase == 0)
+	if (!port->membase)
 		return -ENODEV;
 
 	if (options)