Lockdep reports a bogus possible deadlock on MT8192 Chromebooks due to
the following lock sequences:

1. lock(i2c_register_adapter) [1]; lock(&ec_dev->lock)
2. lock(&ec_dev->lock); lock(prepare_lock);

The actual dependency chains are much longer. The shortened version
looks somewhat like:

1. cros-ec-rpmsg on mtk-scp
   ec_dev->lock -> prepare_lock
2. In rt5682_i2c_probe() on native I2C bus:
   prepare_lock -> regmap->lock -> (possibly) i2c_adapter->bus_lock
3. In rt5682_i2c_probe() on native I2C bus:
   regmap->lock -> i2c_adapter->bus_lock
4. In sbs_probe() on i2c-cros-ec-tunnel I2C bus attached on cros-ec:
   i2c_adapter->bus_lock -> ec_dev->lock

While lockdep is correct that the shared lockdep classes have a circular
dependency, it is bogus because

  a) 2+3 happen on a native I2C bus
  b) 4 happens on the actual EC on ChromeOS devices
  c) 1 happens on the SCP coprocessor on MediaTek Chromebooks that just
     happens to expose a cros-ec interface, but does not have an
     i2c-cros-ec-tunnel I2C bus

In short, the "dependencies" are actually on different devices.

Setup a per-device lockdep key for cros_ec devices so lockdep can tell
the two instances apart. This helps with getting rid of the bogus
lockdep warning. For ChromeOS devices that only have one cros-ec
instance this doesn't change anything.

Also add a missing mutex_destroy, just to make the teardown complete.

[1] This is likely the per I2C bus lock with shared lockdep class
Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
Link: https://lore.kernel.org/r/20230111074146.2624496-1-wenst@chromium.org