iio: common: ssp_sensors: drop conditional optimization for simplicity

Drop conditional in favor of always calculating the timestamp value.
This simplifies the code and allows to drop usage of internal private
variable "scan_timestamp" of the struct iio_dev.

Signed-off-by: Vasileios Amoiridis <vassilisamir@gmail.com>
Link: https://patch.msgid.link/20241214191421.94172-4-vassilisamir@gmail.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>