ALSA: firewire-motu: drop EPOLLOUT from poll return values as write is not supported

The ALSA HwDep character device of the firewire-motu driver incorrectly
returns EPOLLOUT in poll(2), even though the driver implements no operation
for write(2). This misleads userspace applications to believe write() is
allowed, potentially resulting in unnecessarily wakeups.

This issue dates back to the driver's initial code added by a commit
71c3797 ("ALSA: firewire-motu: add hwdep interface"), and persisted
when POLLOUT was updated to EPOLLOUT by a commit a9a0884 ('vfs: do
bulk POLL* -> EPOLL* replacement("").').

This commit fixes the bug.

Signed-off-by: Takashi Sakamoto <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Takashi Iwai <[email protected]>

Author: takaswie

sound/firewire/motu/motu-hwdep.c

@@ -111,7 +111,7 @@ static __poll_t hwdep_poll(struct snd_hwdep *hwdep, struct file *file,
 		events = 0;
 	spin_unlock_irq(&motu->lock);
 
-	return events | EPOLLOUT;
+	return events;
 }
 
 static int hwdep_get_info(struct snd_motu *motu, void __user *arg)