iio: core: Avoid double minus in sysfs output

This patch fixes the issue with double minus in output when
reading channels from sysfs for IIO_VAL_INT_PLUS_MICRO and
IIO_VAL_INT_PLUS_NANO cases. Until this patch if val and val2
both are negatives output string contains "--" before
digits. It is result of "-%d..." in sprintf() format.
Signed-off-by: Oleksandr Kravchenko <o.v.kravchenko@globallogic.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/industrialio-core.c

@@ -383,14 +383,14 @@ static ssize_t iio_read_channel_info(struct device *dev,
 		scale_db = true;
 	case IIO_VAL_INT_PLUS_MICRO:
 		if (val2 < 0)
-			return sprintf(buf, "-%d.%06u%s\n", val, -val2,
+			return sprintf(buf, "-%ld.%06u%s\n", abs(val), -val2,
 				scale_db ? " dB" : "");
 		else
 			return sprintf(buf, "%d.%06u%s\n", val, val2,
 				scale_db ? " dB" : "");
 	case IIO_VAL_INT_PLUS_NANO:
 		if (val2 < 0)
-			return sprintf(buf, "-%d.%09u\n", val, -val2);
+			return sprintf(buf, "-%ld.%09u\n", abs(val), -val2);
 		else
 			return sprintf(buf, "%d.%09u\n", val, val2);
 	case IIO_VAL_FRACTIONAL: