iommu: Fix reference count leak in iommu_group_alloc.

[ Upstream commit 7cc31613 ]

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: Qiushi Wu <wu000273@umn.edu>
Link: https://lore.kernel.org/r/20200527210020.6522-1-wu000273@umn.edu
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>