drivers counter nrfx RTC: Fix ISR prototype

The ISR prototype is not matching the
signature for interrupt handlers, which results in
build warnings.
Let's fix it.

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

drivers/counter/counter_nrfx_rtc.c

@@ -645,8 +645,10 @@ static void alarm_irq_handle(const struct device *dev, uint32_t chan)
 	}
 }
 
-static void irq_handler(const struct device *dev)
+static void irq_handler(const void *arg)
 {
+	const struct device *dev = arg;
+
 	top_irq_handle(dev);
 
 	for (uint32_t i = 0; i < counter_get_num_of_channels(dev); i++) {