iio: Do not accept multiple '.' in fixed point numbers

Currently when parsing a fix-point number we silently skip any additional '.'
found in the string.  E.g. '1.2.3.4' gets parsed as '1.234'. This patch
disallows this and returns an error if more than one '.' is encountered.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/industrialio-core.c

@@ -454,7 +454,7 @@ static ssize_t iio_write_channel_info(struct device *dev,
 				break;
 			else
 				return -EINVAL;
-		} else if (*buf == '.') {
+		} else if (*buf == '.' && integer_part) {
 			integer_part = false;
 		} else {
 			return -EINVAL;