iommu/vt-d: Fix mm reference leak

mainline inclusion
from mainline-v5.7-rc1
commit 902baf61
category: bugfix
bugzilla: 34102
CVE: NA

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Move canonical address check before mmget_not_zero() to avoid mm
reference leak.

Fixes: 9d8c3af3 ("iommu/vt-d: IOMMU Page Request needs to check if address is canonical.")
Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Acked-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Reviewed-by: Hanjun Guo <guohanjun@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>