iommu/amd: Drop pasid_state reference in ppr_notifer error path

In case we are not able to allocate a fault structure a
reference to the pasid_state will be leaked. Fix that by
dropping the reference in the error path in case we hold
one.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Tested-by: Oded Gabbay <Oded.Gabbay@amd.com>