drivers: ieee802154_nrf5: Fix warning in ISR prototype

The ISR prototype was changed some time ago
(6df8b399)
to (const void*) => fix the prototype used when
CONFIG_IEEE802154_NRF5_EXT_IRQ_MGMT is not set
to avoid a compile warning.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>