driver: arcv2_timer0.c: minor changes according to review
driver: arcv2_timer0.c: minor changes according to review

* code style and comment clean up

Signed-off-by: Wayne Ren <d5c6d7c4aa45e53f819f17870783d153a32ba7d0@synopsys.com>

finikorg/zephyr,zephyrproject-rtos/zephyr,punitvara/zephyr,ldts/zephyr,punitvara/zephyr,finikorg/zephyr,ldts/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,explora26/zephyr,galak/zephyr,nashif/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,punitvara/zephyr,nashif/zephyr,Vudentz/zephyr,nashif/zephyr,finikorg/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,punitvara/zephyr,Vudentz/zephyr,Vudentz/zephyr,Vudentz/zephyr,Vudentz/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,punitvara/zephyr,nashif/zephyr