iio: in2xx-adc: 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/adc/ina2xx-adc.c

@@ -550,7 +550,7 @@ static ssize_t ina2xx_allow_async_readout_store(struct device *dev,
 	bool val;
 	int ret;
 
-	ret = strtobool((const char *) buf, &val);
+	ret = strtobool(buf, &val);
 	if (ret)
 		return ret;