hwmon: (iio_hwmon) Fix null pointer dereference

This patch fixes the null pointer dereference in goto error_release_channels
path when allocate memory for st fails.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/iio_hwmon.c

@@ -161,7 +161,7 @@ static int iio_hwmon_probe(struct platform_device *pdev)
 error_remove_group:
 	sysfs_remove_group(&dev->kobj, &st->attr_group);
 error_release_channels:
-	iio_channel_release_all(st->channels);
+	iio_channel_release_all(channels);
 	return ret;
 }