iio: gts: fix infinite loop for gain_to_scaletables()

In iio_gts_build_avail_time_table(), it is checked that gts->num_itime is
non-zero, but gts->num_itime is not checked in gain_to_scaletables(). The
variable time_idx is initialized as gts->num_itime - 1. This implies that
time_idx might initially be set to -1 (0 - 1 = -1). Consequently, using
while (time_idx--) could lead to an infinite loop.

Cc: stable@vger.kernel.org # v6.6+
Fixes: 38416c28 ("iio: light: Add gain-time-scale helpers")
Signed-off-by: Zicheng Qu <quzicheng@huawei.com>
Reviewed-by: Matti Vaittinen <mazziesaccount@gmail.com>
Link: https://patch.msgid.link/20241031014626.2313077-1-quzicheng@huawei.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>