iommu/vt-d: Fix dereference of pointer info before it is null checked

iommu/vt-d: Fix dereference of pointer info before it is null checked

The assignment of iommu from info->iommu occurs before info is null checked
hence leading to a potential null pointer dereference issue. Fix this by
assigning iommu and checking if iommu is null after null checking info.

Addresses-Coverity: ("Dereference before null check")
Fixes: 4c82b88696ac ("iommu/vt-d: Allocate/register iopf queue for sva devices")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20210611135024.32781-1-colin.king@canonical.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>