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: NZhen Lei <thunder.leizhen@huawei.com>
Acked-by: NWill Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20210513075815.6382-1-thunder.leizhen@huawei.comSigned-off-by: NJoerg Roedel <jroedel@suse.de>

drivers/iommu/iommu.c

@@ -3059,9 +3059,6 @@ static int iommu_change_dev_def_domain(struct iommu_group *group,
 	int ret, dev_def_dom;
 	struct device *dev;
 
-	if (!group)
-		return -EINVAL;
-
 	mutex_lock(&group->mutex);
 
 	if (group->default_domain != group->domain) {