ASoC: max98090: revert "ASoC: max98090: fix lockdep warning"

ASoC: max98090: revert "ASoC: max98090: fix lockdep warning"

Commit 2dc98af62c32 ("ASoC: max98090: fix lockdep warning") introduced
a helpful-less small lock: shdn_lock.  Reverts the commit.

Reasons:

1. Lockdep should not be happy by either the original or current code.
From lockdep's point of view, there is a lock inversion anyway.

Let d = dapm_mutex, c = controls_rwsem, s = shdn_lock,

From the reported calling stack: lock acquisition order of
snd_soc_register_card() is: d -> c.
> snd_ctl_add_replace+0x3c/0x84
> dapm_create_or_share_kcontrol+0x24c/0x2e0
> snd_soc_dapm_new_widgets+0x308/0x594
> snd_soc_bind_card+0x80c/0xad4
> devm_snd_soc_register_card+0x34/0x6c

If calling snd_soc_dapm_put_enum_double() in kcontrol's put (e.g.
SOC_DAPM_ENUM_EXT), lock acquisition order is: c -> d.  Note that,
snd_soc_dapm_put_enum_double() acquires d.

The possible lock inversion is always there if registering sound card
and putting mixer control happen at the same time.  In fact, it never
happens because the control device don't show up to the userspace until
the sound card build success.

Commit 2dc98af62c32 ("ASoC: max98090: fix lockdep warning") changes the
order to: c -> s -> d.  The lock inversion is still there.

2. Commit 62d5ae4cafb7 ("ASoC: max98090: save and restore SHDN when
changing sensitive registers SHDN bit") designed to use dapm_mutex to
protect SHDN bit.  Use a separate lock breaks the protection.

DAPM changes SHDN bit automatically when it finds the path.  Thus, any
code wants to change the SHDN bit, need to acquire the dapm_mutex first.

> SND_SOC_DAPM_SUPPLY("SHDN", M98090_REG_DEVICE_SHUTDOWN,
>        M98090_SHDNN_SHIFT, 0, NULL, 0),

Fixes: 2dc98af62c32 ("ASoC: max98090: fix lockdep warning")
Signed-off-by: Tzung-Bi Shih <tzungbi@google.com>
Link: https://lore.kernel.org/r/20200117073814.82441-2-tzungbi@google.com
Signed-off-by: Mark Brown <broonie@kernel.org>