fix(serial): Fix serial_flush_from_isr always yielding

By passing `&resched` instead of just `resched`, the internal comparison
in FreeRTOS would always evaluate to rescheduling.  Curiously, only some
GCC versions emit the -Waddress warning for this while others do not ...

Signed-off-by: Rahix <rahix@rahix.de>

epicardium/modules/serial.c

@@ -161,7 +161,7 @@ static void serial_flush_from_isr(void)
 
 	taskEXIT_CRITICAL_FROM_ISR(basepri);
 
-	portYIELD_FROM_ISR(&resched);
+	portYIELD_FROM_ISR(resched);
 }
 
 static void serial_flush_from_thread(void)