iio: accel: sca3300: fix uninitialized iio scan data

Fix potential leak of uninitialized stack data to userspace by ensuring
that the `channels` array is zeroed before use.

Fixes: edeb67fb ("iio: accel: sca3300: use IIO_DECLARE_BUFFER_WITH_TS")
Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20250723-iio-accel-sca3300-fix-uninitialized-iio-scan-data-v1-1-12dbfb3307b7@baylibre.com


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