iio: as3935: Remove unnecessary cast

`buf` is cast to a const char *, but `buf` is already a const char *, so
the case is unnecessary.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/proximity/as3935.c

@@ -133,7 +133,7 @@ static ssize_t as3935_sensor_sensitivity_store(struct device *dev,
 	unsigned long val;
 	int ret;
 
-	ret = kstrtoul((const char *) buf, 10, &val);
+	ret = kstrtoul(buf, 10, &val);
 	if (ret)
 		return -EINVAL;