serial: altera: set RRDY flag also without irq

The UART can be operated without an irq. In this case a timer is setup
that regularily calls altera_uart_interrupt(). The receiving part
depends on pp->imr having the bit ALTERA_UART_STATUS_RRDY_MSK set,
otherwise altera_uart_rx_chars() is never called. So ensure that the bit
gets set (disguised as ALTERA_UART_CONTROL_RRDY_MSK) by not returning
early from altera_uart_startup() if port->irq is 0.

This doesn't affect the hardware as the ALTERA_UART_CONTROL_RRDY_MSK bit
isn't actually written to the control register.

Signed-off-by: Uwe Kleine-König <[e-mail]>
Acked-by: Tobias Klauser <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/altera_uart.c

···
 {
 	struct altera_uart *pp = container_of(port, struct altera_uart, port);
 	unsigned long flags;
-	int ret;
 
 	if (!port->irq) {
 		timer_setup(&pp->tmr, altera_uart_timer, 0);
 		mod_timer(&pp->tmr, jiffies + uart_poll_timeout(port));
-		return 0;
-	}
+	} else {
+		int ret;
 
-	ret = request_irq(port->irq, altera_uart_interrupt, 0,
-			DRV_NAME, port);
-	if (ret) {
-		pr_err(DRV_NAME ": unable to attach Altera UART %d "
-		       "interrupt vector=%d\n", port->line, port->irq);
-		return ret;
+		ret = request_irq(port->irq, altera_uart_interrupt, 0,
+				DRV_NAME, port);
+		if (ret) {
+			pr_err(DRV_NAME ": unable to attach Altera UART %d "
+			       "interrupt vector=%d\n", port->line, port->irq);
+			return ret;
+		}
 	}
 
 	spin_lock_irqsave(&port->lock, flags);