[SCSI] zfcp: No ERP escalation on gpn_ft eval

If the evaluation of GPN_FT requests wants to remove an invalid port
from the system the zfcp_erp_port_shutdown function is triggered.
Depending on the system status a superior action (e.g. adapter reopen)
is required. This can lead to an invalid mem access of the port struct
which might be freed at the time since the superior action is not
holding a reference of the port which triggered this ERP action.

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@suse.de>