iio: adc: max1363: Use a small fixed size buffer to replace dynamic allocation

iio: adc: max1363: Use a small fixed size buffer to replace dynamic allocation

Drop the recurrent allocation of the data buffer from the trigger
handler and put it in the iio_priv(). This way, the maximum amount of
channels is always allocated in favor of simpler code and drop
of usage of the internal private variable "scan_timestamp" of the
struct iio_dev.

Signed-off-by: Vasileios Amoiridis <vassilisamir@gmail.com>
Link: https://patch.msgid.link/20241214191421.94172-3-vassilisamir@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>