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

In the Linux kernel, the following vulnerability has been resolved: 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.