iio: adc: mt6360-adc: use aligned_s64 for timestamp

iio: adc: mt6360-adc: use aligned_s64 for timestamp

Follow the pattern of other drivers and use aligned_s64 for the
timestamp. This will ensure that the timestamp is correctly aligned on
all architectures. It also ensures that the struct itself it also 8-byte
aligned so we can drop the explicit __aligned(8) attribute.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Link: https://patch.msgid.link/20250417-iio-more-timestamp-alignment-v1-2-eafac1e22318@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>