openvswitch: Fix memory leak in ovs_vport_alloc() error path

ovs_vport_alloc() bails out without freeing the memory 'vport' points to.

Picked up by Coverity - CID 1230503.

Fixes: 5cd667b0 ("openvswitch: Allow each vport to have an array of 'port_id's.")
Signed-off-by: Christoph Jaeger <cj@linux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>