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: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>