ALSA: seq: Fix memory leak at error path in snd_seq_create_port()

We forgot to release a newly allocated item at the error path in
snd_seq_create_port().  This patch fixes it.

Fixes: 7c3f0d3d

 ("ALSA: seq: Check the conflicting port at port creation")
Reported-by:  <syzbot+cf8e7fa4eeec59b3d485@syzkaller.appspotmail.com>
Closes: https://lore.kernel.org/r/00000000000098ed3a0600965f89@google.com
Link: https://lore.kernel.org/r/20230717062555.31592-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>