drivers/timer/nrf_rtc_timer: clarify intent of ZLI compensation
drivers/timer/nrf_rtc_timer: clarify intent of ZLI compensation

The variable enabling entry to the zero latency interrupt compensation
loop was named generically, and its logic inverted, making the code
difficult to understand.  Change the name and initial value to more
clearly indicate its role.

Signed-off-by: Peter Bigot <a4112a160b558d5427af084318038e19a95979ee@nordicsemi.no>

zephyrproject-rtos/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,nashif/zephyr,galak/zephyr,finikorg/zephyr,Vudentz/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,finikorg/zephyr,Vudentz/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,Vudentz/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,nashif/zephyr,finikorg/zephyr,galak/zephyr,Vudentz/zephyr