iio: dummy: iio_simply_dummy_buffer: fix information leak in triggered buffer

iio: dummy: iio_simply_dummy_buffer: fix information leak in triggered buffer

The 'data' array is allocated via kmalloc() and it 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.

Use kzalloc for the memory allocation to avoid pushing uninitialized
information to userspace.

Cc: stable@vger.kernel.org
Fixes: 415f79244757 ("iio: Move IIO Dummy Driver out of staging")
Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Link: https://patch.msgid.link/20241125-iio_memset_scan_holes-v1-9-0cb6e98d895c@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>