iio: pressure: mprls0025pa: use aligned_s64 for timestamp

iio: pressure: mprls0025pa: use aligned_s64 for timestamp

Follow the pattern of other drivers and use aligned_s64 for the
timestamp. This will ensure the struct itself it also 8-byte aligned.

While touching this, convert struct mpr_chan to an anonymous struct
to consolidate the code a bit to make it easier for future readers.

Fixes: 713337d9143e ("iio: pressure: Honeywell mprls0025pa pressure sensor")
Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20250418-iio-more-timestamp-alignment-v2-2-d6a5d2b1c9fe@baylibre.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>