Found when trying to reassemble an active externally managed array.  Without
this check we hit the more noisy "sysfs duplicate" warning in the later call
to kobject_add.
Signed-off-by: NDan Williams <dan.j.williams@intel.com>
Signed-off-by: NNeil Brown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>