scsi: fcoe: pass in fcoe_rport structure instead of fc_rport_priv

Instead of using the generic 'fc_rport_priv' structure as argument and then
having to painstakingly outcast this to fcoe_rport we should be passing the
fcoe_rport structure itself and reduce complexity.
Signed-off-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>