Revert "ALSA: seq: Protect in-kernel ioctl calls with mutex"

[ Upstream commit f0654ba94e33699b295ce4f3dc73094db6209035 ]

This reverts commit feb689025fbb6f0aa6297d3ddf97de945ea4ad32.

The fix attempt was incorrect, leading to the mutex deadlock through
the close of OSS sequencer client.  The proper fix needs more
consideration, so let's revert it now.

Fixes: feb689025fbb ("ALSA: seq: Protect in-kernel ioctl calls with mutex")
Reported-by: syzbot+47ded6c0f23016cde310@syzkaller.appspotmail.com
Signed-off-by: NTakashi Iwai <tiwai@suse.de>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

sound/core/seq/seq_clientmgr.c

@@ -2337,19 +2337,14 @@ int snd_seq_kernel_client_ctl(int clientid, unsigned int cmd, void *arg)
 {
 	const struct ioctl_handler *handler;
 	struct snd_seq_client *client;
-	int err;
 
 	client = clientptr(clientid);
 	if (client == NULL)
 		return -ENXIO;
 
 	for (handler = ioctl_handlers; handler->cmd > 0; ++handler) {
-		if (handler->cmd == cmd) {
-			mutex_lock(&client->ioctl_mutex);
-			err = handler->func(client, arg);
-			mutex_unlock(&client->ioctl_mutex);
-			return err;
-		}
+		if (handler->cmd == cmd)
+			return handler->func(client, arg);
 	}
 
 	pr_debug("ALSA: seq unknown ioctl() 0x%x (type='%c', number=0x%02x)\n",