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

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.

Cc: Lars-Peter Clausen <lars@metafoo.de>
Cc: Michael Hennerich <Michael.Hennerich@analog.com>
Cc: Jonathan Cameron <jic23@kernel.org>
Cc: David Lechner <dlechner@baylibre.com>
Cc: "Nuno Sá" <nuno.sa@analog.com>
Cc: Andy Shevchenko <andy@kernel.org>
Fixes: e4570f4bb231 ("iio: imu: adis16550: align buffers for timestamp")
Cc: stable <stable@kernel.org>
Assisted-by: gregkh_clanker_t1000
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>