iio: accel: mma8452: Rename a struct for code readibility

Rename time step look up struct to generic name
as the values in the look table are same for all
the other events like pulse, transient etc.

Signed-off-by: Harinath Nampally <harinath922@gmail.com>
Acked-by: Martin Kepplinger <martink@posteo.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>