[SCSI] libfc: have rport_create do a lookup for pre-existing rports first

For future discovery patches, change rport_create to return a previously
created rport_priv that has the FC_ID as long as it isn't in deleted state.

Signed-off-by: Joe Eykholt <jeykholt@cisco.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>