iommu/vt-d: Check for allocation failure in aux_detach_device()

In current kernels small allocations never fail, but checking for
allocation failure is the correct thing to do.

Fixes: 18abda7a ("iommu/vt-d: Fix general protection fault in aux_detach_device()")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/YJuobKuSn81dOPLd@mwanda
Link: https://lore.kernel.org/r/20210519015027.108468-2-baolu.lu@linux.intel.comSigned-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/intel/iommu.c

@@ -4606,6 +4606,8 @@ static int auxiliary_link_device(struct dmar_domain *domain,
 
 	if (!sinfo) {
 		sinfo = kzalloc(sizeof(*sinfo), GFP_ATOMIC);
+		if (!sinfo)
+			return -ENOMEM;
 		sinfo->domain = domain;
 		sinfo->pdev = dev;
 		list_add(&sinfo->link_phys, &info->subdevices);