Kobject: change net/bridge to use kobject_create_and_add

The kobject in the bridge code is only used for registering with sysfs,
not for any lifespan rules.  This patch changes it to be only a pointer
and use the simpler api for this kind of thing.

Cc: Stephen Hemminger <shemminger@linux-foundation.org>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>