Documentation: driver core: remove use of BUS_ATTR

We are getting rid of the "raw" BUS_ATTR() macro, so fix up the
documentation to not refer to it anymore.

Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>