openvswitch: small potential memory leak in ovs_vport_alloc()

We're unlikely to hit this leak, but the static checkers complain if we
don't take care of it.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Jesse Gross <jesse@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>