drivers: gpio: nrf: fix pin number used in getting GPIOTE channel
drivers: gpio: nrf: fix pin number used in getting GPIOTE channel

Incorrect GPIOTE channel was being freed because the pin number
being used is not the absolute pin but the pin within the port.

Signed-off-by: Wael Barakat <ad082c287ab7fe66e512d6cad8e912a12f01d22e@gmail.com>

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