iommu/vt-d: fix a loop in prq_event_thread()

There is an extra semi-colon on this if statement so we always break on
the first iteration.

Fixes: 0204a496 ('iommu/vt-d: Add callback to device driver on page faults')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>