[SCSI] zfcp: fix erp timeout cleanup for port open requests

If an open port fsf request times out (in erp) the
corresponding erp_action member of the fsf
request need to set to NULL. If the port structure
will be removed later-on there will be still a
reference in the fsf request to the non existing
erp_action otherwise.

Signed-off-by: Martin Petermann <martin.petermann@de.ibm.com>
Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>