[SCSI] zfcp: Fix fsf_status_read return code handling

If allocation of a status buffer failed the function incorrectly
returned 0 instead of -ENOMEM.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Peschke <mp3@de.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>