iommu: Don't print warning when IOMMU driver only supports unmanaged domains

mainline inclusion
from mainline-v5.1-rc3
commit 8bc32a28
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I72C6P
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8bc32a285660e13fdcf92ddaf5b8653abe112040



-------------------------------------------------

Print the warning about the fall-back to IOMMU_DOMAIN_DMA in
iommu_group_get_for_dev() only when such a domain was
actually allocated.

Otherwise the user will get misleading warnings in the
kernel log when the iommu driver used doesn't support
IOMMU_DOMAIN_DMA and IOMMU_DOMAIN_IDENTITY.

Fixes: fccb4e3b ('iommu: Allow default domain type to be set on the kernel command line')
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Zhang Zekun <zhangzekun11@huawei.com>
Reviewed-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>