[SCSI] zfcp: Prevent usage w/o holding a reference

The ERP got values assigned for which no reference was taken.  This
can lead to an unpredictable race condition.  Fix this by only
assigning the values which are required and for which a reference was
pulled or is held implicitly.

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>