iommufd: Initialize the flags of vevent in iommufd_viommu_report_event()

The vevent->header.flags is not initialized per allocation, hence the
vevent read path may treat the vevent as lost_events_header wrongly.
Use kzalloc() to alloc memory for new vevent.

Fixes: e8e1ef9 ("iommufd/viommu: Add iommufd_viommu_report_event helper")
Link: https://patch.msgid.link/r/20250324120034.5940-2-yi.l.liu@intel.com
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

Author: yiliu1765

drivers/iommu/iommufd/driver.c

@@ -102,7 +102,7 @@ int iommufd_viommu_report_event(struct iommufd_viommu *viommu,
 		goto out_set_header;
 	}
 
-	vevent = kmalloc(struct_size(vevent, event_data, data_len), GFP_ATOMIC);
+	vevent = kzalloc(struct_size(vevent, event_data, data_len), GFP_ATOMIC);
 	if (!vevent) {
 		rc = -ENOMEM;
 		vevent = &veventq->lost_events_header;