tests: drivers: timer: nrf_rtc_timer: Minor fixes
tests: drivers: timer: nrf_rtc_timer: Minor fixes

Changed chan type to int in the test_timeout function which follows
change in the api to always use int for channel parameter.

Added assert to check that channel was successfully allocated in
test_resetting_cc().

Signed-off-by: Krzysztof Chruscinski <9b6dc988558c51b0405b49b55c8e66862969844b@nordicsemi.no>

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