iio: iio_format_value(): Use signed temporary for IIO_VAL_FRACTIONAL_LOG2

IIO_VAL_FRACTIONAL_LOG2 works with signed values, yet the temporary we use
is unsigned. This works at the moment because the variable is implicitly
cast to signed everywhere where it is used.

But it will certainly be cleaner to use a signed variable in the first
place.
Signed-off-by: NLars-Peter Clausen <lars@metafoo.de>
Link: https://lore.kernel.org/r/20201215191743.2725-1-lars@metafoo.deSigned-off-by: NJonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/industrialio-core.c

@@ -625,7 +625,6 @@ EXPORT_SYMBOL(iio_read_mount_matrix);
 static ssize_t __iio_format_value(char *buf, size_t len, unsigned int type,
 				  int size, const int *vals)
 {
-	unsigned long long tmp;
 	int tmp0, tmp1;
 	s64 tmp2;
 	bool scale_db = false;
@@ -658,8 +657,8 @@ static ssize_t __iio_format_value(char *buf, size_t len, unsigned int type,
 		else
 			return snprintf(buf, len, "%d.%09u", tmp0, abs(tmp1));
 	case IIO_VAL_FRACTIONAL_LOG2:
-		tmp = shift_right((s64)vals[0] * 1000000000LL, vals[1]);
-		tmp0 = (int)div_s64_rem(tmp, 1000000000LL, &tmp1);
+		tmp2 = shift_right((s64)vals[0] * 1000000000LL, vals[1]);
+		tmp0 = (int)div_s64_rem(tmp2, 1000000000LL, &tmp1);
 		return scnprintf(buf, len, "%d.%09u", tmp0, abs(tmp1));
 	case IIO_VAL_INT_MULTIPLE:
 	{