IB/iser: Handle fastreg/local_inv completion errors

Fast registration and local invalidate work requests can
also fail. We should call error completion handler for them.

Reported-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>