iio: event_monitor: Flush output on event

By flushing the output, iio_event_monitor can be more useful to programs
chained along with it.

  iio_event_monitor stk3310 | awk '/rising/{system("my_unlockscreen.sh")} /falling/{system("my_lockscreen.sh")}'

Without this flush, the above example would buffer a number of events,
then after a while run the lock/unlock scripts several times.
Signed-off-by: Zach DeCook <zachdecook@librem.one>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

tools/iio/iio_event_monitor.c

@@ -279,6 +279,7 @@ static void print_event(struct iio_event_data *event)
 		printf(", direction: %s", iio_ev_dir_text[dir]);
 
 	printf("\n");
+	fflush(stdout);
 }
 
 /* Enable or disable events in sysfs if the knob is available */