drivers: timer: nrf_rtc: Use correct macro when capping cycles

When checking the absolute value of cycles set to the comparator
use the MAX_CYCLES instead of MAX_TICKS.

The commit changes function names and comments to make it clear
where ticks (system ticks) and where RTC cycles are used.

Fixes #26701

Signed-off-by: Pawel Dunaj <pawel.dunaj@nordicsemi.no>