driver: counter: counter_ll_stm32_rtc.c: Add 1 tick to alarm
driver: counter: counter_ll_stm32_rtc.c: Add 1 tick to alarm

Add +1 tick to alarm in order to compensate the partially started tick.
Alarm will expire between requested ticks and ticks+1.
In case only 1 tick is requested, it will avoid that +1 Tick event
occurs before alarm setting is finished.

Signed-off-by: Alexandre Bourdiol <c23cc711c078d3e6bb50b3dc45a1b8842691e59a@st.com>

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