kobject: grab the kset reference in kobject_add, not kobject_init

kobject_init should not be grabing any references, but only initializing
the object.  This patch fixes this, and makes the lock hold-time shorter
for when a kset is present in the kobject.

The current kernel tree has been audited to verify that this change
should be safe.

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