serial: fix test of unsigned

The variables were unsigned so the tests did not work.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/serial/timbuart.c b/drivers/serial/timbuart.c
index 34b31da0..7bf1026 100644
--- a/drivers/serial/timbuart.c
+++ b/drivers/serial/timbuart.c
@@ -421,7 +421,7 @@
 
 static int timbuart_probe(struct platform_device *dev)
 {
-	int err;
+	int err, irq;
 	struct timbuart_port *uart;
 	struct resource *iomem;
 
@@ -453,11 +453,12 @@
 	uart->port.mapbase = iomem->start;
 	uart->port.membase = NULL;
 
-	uart->port.irq = platform_get_irq(dev, 0);
-	if (uart->port.irq < 0) {
+	irq = platform_get_irq(dev, 0);
+	if (irq < 0) {
 		err = -EINVAL;
 		goto err_register;
 	}
+	uart->port.irq = irq;
 
 	tasklet_init(&uart->tasklet, timbuart_tasklet, (unsigned long)uart);