atmel_serial: Fix build on avr32 with CONFIG_PM enabled

AVR32 doesn't have at91_suspend_entering_slow_clock(). Just assume the
clock will keep running for now.

David has a better solution for this, but this works for now. Leaving
the USART clock running won't prevent the PM code from entering deep
power-down modes anyway.

Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>
Cc: David Brownell <david-b@pacbell.net>
Cc: Andrew Victor <linux@maxim.org.za>

drivers/serial/atmel_serial.c

@@ -1439,14 +1439,23 @@ static struct uart_driver atmel_uart = {
 };
 
 #ifdef CONFIG_PM
+static bool atmel_serial_clk_will_stop(void)
+{
+#ifdef CONFIG_ARCH_AT91
+	return at91_suspend_entering_slow_clock();
+#else
+	return false;
+#endif
+}
+
 static int atmel_serial_suspend(struct platform_device *pdev,
 				pm_message_t state)
 {
 	struct uart_port *port = platform_get_drvdata(pdev);
 	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
 
 	if (device_may_wakeup(&pdev->dev)
-	    && !at91_suspend_entering_slow_clock())
+	    && !atmel_serial_clk_will_stop())
 		enable_irq_wake(port->irq);
 	else {
 		uart_suspend_port(&atmel_uart, port);