[SCSI] zfcp: avoid double notify in lowmem scenario

In a LOWMEM condition an ERP notification would have been sent twice
causing an unpredictable behaviour of the ERP.

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>