scsi: lpfc: Fix lpfc_wwn_set return code check

When I reversed the patch to re-add the lpfc_soft_wwn parameter feature,
it re-added code that had a long-standing bug. (that's what I get I
guess :)

As Dan Carpenter pointed out - error checks looked at wrong polarity.  0
is success, -errno is failure. Updated checks.

Signed-off-by: James Smart <james.smart@broadcom.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>