hiddev: Return EPOLLOUT from hiddev_poll

Always return EPOLLOUT from hiddev_poll when a device is connected.
This is safe since hiddev_write always fails and improves compatibility
with tools like socat.
Signed-off-by: Fabian Henneke <fabian@henneke.me>
In-reply-to: <nycvar.YFH.7.76.1907171333160.5899@cbobk.fhfr.pm>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/usbhid/hiddev.c

@@ -416,7 +416,7 @@ static __poll_t hiddev_poll(struct file *file, poll_table *wait)
 
 	poll_wait(file, &list->hiddev->wait, wait);
 	if (list->head != list->tail)
-		return EPOLLIN | EPOLLRDNORM;
+		return EPOLLIN | EPOLLRDNORM | EPOLLOUT;
 	if (!list->hiddev->exist)
 		return EPOLLERR | EPOLLHUP;
 	return 0;