kobject_init_and_add() takes reference even when it fails.
Thus, when kobject_init_and_add() returns an error,
kobject_put() must be called to properly clean up the kobject.

Fixes: d72e31c9 ("iommu: IOMMU Groups")
Signed-off-by: NQiushi Wu <wu000273@umn.edu>
Link: https://lore.kernel.org/r/20200527210020.6522-1-wu000273@umn.eduSigned-off-by: NJoerg Roedel <jroedel@suse.de>