iio: adc: ti-ads8688: fix information leak in triggered buffer

iio: adc: ti-ads8688: fix information leak in triggered buffer

The 'buffer' local array is used to push data to user space from a
triggered buffer, but it does not set values for inactive channels, as
it only uses iio_for_each_active_channel() to assign new values.

Initialize the array to zero before using it to avoid pushing
uninitialized information to userspace.

Cc: stable@vger.kernel.org
Fixes: 61fa5dfa5f52 ("iio: adc: ti-ads8688: Fix alignment of buffer in iio_push_to_buffers_with_timestamp()")
Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Link: https://patch.msgid.link/20241125-iio_memset_scan_holes-v1-8-0cb6e98d895c@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>