[SCSI] zfcp: Fix reference counter for remote ports

Fix the remote port reference counter handling during ELS ADISC
commands and find the remote port by WWPN not by D_IDs that could
change.

Signed-off-by: Swen Schillig <swen@vnet.ibm.com>
Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>