iio: imu: adis16550: fix stack leak in trigger handler

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

iio: imu: adis16550: fix stack leak in trigger handler

adis16550_trigger_handler() declares the scan data array on the stack

without initializing it. The memcpy() at the bottom fills only the

first 28 bytes (TEMP + 6 channels of GYRO/ACCEL data), and

iio_push_to_buffers_with_timestamp() writes the s64 timestamp at the

8-byte-aligned offset 32. Bytes 28-31 remain uninitialized stack data

which leaks to userspace on ever trigger.

Fix this all by just zero-initializing the structure on the stack.