device-core: Kill the lockdep_mutex

Per Peter [1], the lockdep API has native support for all the use cases
lockdep_mutex was attempting to enable. Now that all lockdep_mutex users
have been converted to those APIs, drop this lock.

Link: https://lore.kernel.org/r/[e-mail] [1]
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: "Rafael J. Wysocki" <[e-mail]>
Suggested-by: Peter Zijlstra <[e-mail]>
Reviewed-by: Ira Weiny <[e-mail]>
Acked-by: Greg Kroah-Hartman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dan Williams <[e-mail]>

drivers/base/core.c

···
 	kobject_init(&dev->kobj, &device_ktype);
 	INIT_LIST_HEAD(&dev->dma_pools);
 	mutex_init(&dev->mutex);
-#ifdef CONFIG_PROVE_LOCKING
-	mutex_init(&dev->lockdep_mutex);
-#endif
 	lockdep_set_novalidate_class(&dev->mutex);
 	spin_lock_init(&dev->devres_lock);
 	INIT_LIST_HEAD(&dev->devres_head);

include/linux/device.h

···
  * 		This identifies the device type and carries type-specific
  * 		information.
  * @mutex:	Mutex to synchronize calls to its driver.
- * @lockdep_mutex: An optional debug lock that a subsystem can use as a
- * 		peer lock to gain localized lockdep coverage of the device_lock.
  * @bus:	Type of bus device is on.
  * @driver:	Which driver has allocated this
  * @platform_data: Platform data specific to the device.
···
 					   core doesn't touch it */
 	void		*driver_data;	/* Driver data, set and get with
 					   dev_set_drvdata/dev_get_drvdata */
-#ifdef CONFIG_PROVE_LOCKING
-	struct mutex		lockdep_mutex;
-#endif
 	struct mutex		mutex;	/* mutex to synchronize calls to
 					 * its driver.
 					 */