iio: gts-helper: Fix memory leaks for the error path of iio_gts_build_avail_scale_table()
In the Linux kernel, the following vulnerability has been resolved:

iio: gts-helper: Fix memory leaks for the error path of iio_gts_build_avail_scale_table()

If per_time_scales[i] or per_time_gains[i] kcalloc fails in the for loop
of iio_gts_build_avail_scale_table(), the err_free_out will fail to call
kfree() each time when i is reduced to 0, so all the per_time_scales[0]
and per_time_gains[0] will not be freed, which will cause memory leaks.

Fix it by checking if i >= 0.