iio: imu: inv_icm42600: switch timestamp type from int64_t __aligned(8) to aligned_s64

iio: imu: inv_icm42600: switch timestamp type from int64_t __aligned(8) to aligned_s64

The vast majority of IIO drivers use aligned_s64 for the type of the
timestamp field.  It is not a bug to use int64_t and until this series
iio_push_to_buffers_with_timestamp() took and int64_t timestamp, it
is inconsistent.  This change is to remove that inconsistency and
ensure there is one obvious choice for future drivers.

Acked-by: Jean-Baptiste Maneyrol <jean-baptiste.maneyrol@tdk.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20241215182912.481706-19-jic23@kernel.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>