[SCSI] zfcp: returning an ERR_PTR where a NULL value is expected

Aborting a SCSI cmnd might requrie to send a abort_fsf_cmnd. If the
creation of this fsf_req fails an ERR_PTR is returned where a NULL
value would be expected as an error indicator. This ERR_PTR is
dereferenced as valid fsf_req in succeeding processing leading to
an error.

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>