iommu: Don't take group reference in iommu_alloc_default_domain()

iommu: Don't take group reference in iommu_alloc_default_domain()

The iommu_alloc_default_domain() function takes a reference to an IOMMU
group without releasing it. This causes the group to never be released,
with undefined side effects.

The function has only one call-site, which takes a group reference on
its own, so to fix this leak, do not take another reference in
iommu_alloc_default_domain() and pass the group as a function parameter
instead.

Fixes: 6e1aa2049154 ("iommu: Move default domain allocation to iommu_probe_device()")
Reported-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Tested-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Cc: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Link: https://lore.kernel.org/r/20200525130122.380-1-joro@8bytes.org
Reference: https://lore.kernel.org/lkml/20200522130145.30067-1-saiprakash.ranjan@codeaurora.org/