ALSA: seq: Use auto-cleanup for client refcounting

ALSA: seq: Use auto-cleanup for client refcounting

The current code manages the refcount of client in a way like:

	snd_seq_client *client;
	client = clientptr(id);
	....
	snd_seq_client_unlock(client);

Now we introduce an auto-cleanup macro to manage the unlock
implicitly, namely, the above will be replaced like:

	snd_seq_client *client __free(snd_seq_client) = NULL;
	client = clientptr(id);

and we can forget the unref call.

A part of the code in snd_seq_deliver_single_event() is factored out
to a function, so that the auto-cleanups can be applied cleanly.

This also allows us to replace some left mutex lock/unlock with
guard(), and also reduce scoped_guard() to the normal guard(), too.

Only code refactoring, and no behavior change.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://patch.msgid.link/20250827080520.7544-5-tiwai@suse.de