Warn user when current-speed property isn't set and exit.

Signed-off-by: Clemens Koller <clemens.koller@anagramm.de>
CC: Arnd Bergmann <arnd@arndb.de>

diff --git a/drivers/serial/of_serial.c b/drivers/serial/of_serial.c
index a64d858..e035cb2 100644
--- a/drivers/serial/of_serial.c
+++ b/drivers/serial/of_serial.c
@@ -36,6 +36,10 @@ static int __devinit of_platform_serial_setup(struct of_device *ofdev,
 	memset(port, 0, sizeof *port);
 	spd = of_get_property(np, "current-speed", NULL);
 	clk = of_get_property(np, "clock-frequency", NULL);
+	if (!spd) {
+		dev_warn(&ofdev->dev, "no current-speed property set\n");
+		return -ENODEV;
+	}
 	if (!clk) {
 		dev_warn(&ofdev->dev, "no clock-frequency property set\n");
 		return -ENODEV;