driver core: bus: move documentation for lock_key to proper location.

In commit 37e98d9b ("driver core: bus: move lock_class_key into
dynamic structure"), the lock_key variable moved out of struct bus_type
and into struct subsys_private, yet the documentation for it did not
move.  Fix that up and place the documentation comment in the correct
location.

Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Fixes: 37e98d9b ("driver core: bus: move lock_class_key into dynamic structure")
Link: https://lore.kernel.org/r/20230324090814.386654-1-gregkh@linuxfoundation.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>