iommu: Delete a duplicate check in iommu_change_dev_def_domain()

Function iommu_group_store_type() is the only caller of the static
function iommu_change_dev_def_domain() and has performed
"if (WARN_ON(!group))" detection before calling it. So the one here is
redundant.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20210513075815.6382-1-thunder.leizhen@huawei.com


Signed-off-by: Joerg Roedel <jroedel@suse.de>