tty: serial: lpc32xx_hs: fix handling platform_get_irq result

The function can return negative values.

The problem has been detected using proposed semantic patch
scripts/coccinelle/tests/unsigned_lesser_than_zero.cocci [1].

[1]: http://permalink.gmane.org/gmane.linux.kernel/2038576

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/lpc32xx_hs.c

@@ -691,12 +691,13 @@ static int serial_hs_lpc32xx_probe(struct platform_device *pdev)
 	p->port.mapbase = res->start;
 	p->port.membase = NULL;
 
-	p->port.irq = platform_get_irq(pdev, 0);
-	if (p->port.irq < 0) {
+	ret = platform_get_irq(pdev, 0);
+	if (ret < 0) {
 		dev_err(&pdev->dev, "Error getting irq for HS UART port %d\n",
 			uarts_registered);
-		return p->port.irq;
+		return ret;
 	}
+	p->port.irq = ret;
 
 	p->port.iotype = UPIO_MEM32;
 	p->port.uartclk = LPC32XX_MAIN_OSC_FREQ;