Staging: iio/adc: strict_strtoul was used with a long type variable

The function ad7280_store_balance_timer() parses data from a char*
buffer into a long variable, but uses the the function strict_strtoul
which expects a pointer to an unsigned long variable as its third
parameter.

As Dan Carpenter mentioned, the values are capped a few lines later,
but a check if val is negative is missing.
Now this function will return -ERANGE if there is a representation of
a negative number in buf.

Additionally the checkpatch.pl considers strict_strtoul as obsolete.
I replaced its call with the suggested kstrtoul.
Signed-off-by: Andreas Ruprecht <rupran@einserver.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/iio/adc/ad7280a.c

@@ -456,10 +456,10 @@ static ssize_t ad7280_store_balance_timer(struct device *dev,
 	struct iio_dev *indio_dev = dev_get_drvdata(dev);
 	struct ad7280_state *st = iio_priv(indio_dev);
 	struct iio_dev_attr *this_attr = to_iio_dev_attr(attr);
-	long val;
+	unsigned long val;
 	int ret;
 
-	ret = strict_strtoul(buf, 10, &val);
+	ret = kstrtoul(buf, 10, &val);
 	if (ret)
 		return ret;