scsi: scsi_transport_fc: return -EBUSY for deleted vport

When trying to delete a vport via 'vport_delete' sysfs attribute we
should be checking if the port is already in state VPORT_DELETING; if so
there's no need to do anything.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>