zephyrSerial: Keeping up with UART API changes

Update for uart_irq_update() changes introduced with
zephyrproject-rtos/zephyr#105231.

Signed-off-by: TOKITA Hiroshi <tokita.hiroshi@gmail.com>

Author: soburi

cores/arduino/zephyrSerial.cpp

@@ -68,9 +68,7 @@ void arduino::ZephyrSerial::IrqHandler() {
 	int length;
 	int ret = 0;
 
-	if (!uart_irq_update(uart)) {
-		return;
-	}
+	(void)uart_irq_update(uart);
 
 	if (ring_buf_size_get(&tx.ringbuf) == 0) {
 		uart_irq_tx_disable(uart);