tools: iio: iio_utils: fix digit calculation

The iio_utils uses a digit calculation in order to know length of the
file name containing a buffer number. The digit calculation does not
work for number 0.

This leads to allocation of one character too small buffer for the
file-name when file name contains value '0'. (Eg. buffer0).

Fix digit calculation by returning one digit to be present for number
'0'.

Fixes: 096f9b862e ("tools:iio:iio_utils: implement digit calculation")
Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Link: https://lore.kernel.org/r/Y0f+tKCz+ZAIoroQ@dc75zzyyyyyyyyyyyyycy-3.rev.dnainternet.fi
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

tools/iio/iio_utils.c

@@ -547,6 +547,10 @@ static int calc_digits(int num)
 {
 	int count = 0;
 
+	/* It takes a digit to represent zero */
+	if (!num)
+		return 1;
+
 	while (num != 0) {
 		num /= 10;
 		count++;