serial: samsung: protect NULL dereference of clock name

When priting the serial clock source, if clock source name is null,
kernel reference NULL point.

Signed-off-by: KeyYoung Park <keyyoung.park@samsung.com>
Signed-off-by: Huisung Kang <hs1218.kang@samsung.com>
Signed-off-by: Kyoungil Kim <ki0351.kim@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/samsung.c

@@ -1162,7 +1162,8 @@ static ssize_t s3c24xx_serial_show_clksrc(struct device *dev,
 	if (IS_ERR(ourport->baudclk))
 		return -EINVAL;
 
-	return snprintf(buf, PAGE_SIZE, "* %s\n", ourport->baudclk->name);
+	return snprintf(buf, PAGE_SIZE, "* %s\n",
+			ourport->baudclk->name ?: "(null)");
 }
 
 static DEVICE_ATTR(clock_source, S_IRUGO, s3c24xx_serial_show_clksrc, NULL);