Input: evdev - try to wake up readers only if we have full packet

We should only wake waiters on the event device when we actually post
an EV_SYN/SYN_REPORT to the queue. Otherwise we end up making waiting
threads runnable only to go right back to sleep because the device
still isn't readable.
Reported-by: Jeffrey Brown <jeffbrown@android.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

drivers/input/evdev.c

@@ -111,7 +111,8 @@ static void evdev_event(struct input_handle *handle,
 
 	rcu_read_unlock();
 
-	wake_up_interruptible(&evdev->wait);
+	if (type == EV_SYN && code == SYN_REPORT)
+		wake_up_interruptible(&evdev->wait);
 }
 
 static int evdev_fasync(int fd, struct file *file, int on)