scsi: qla2xxx: Silence a static checker warning

Smatch and Clang both complain that LOGIN_TEMPLATE_SIZE is more than
sizeof(ha->plogi_els_payld.fl_csp).

Smatch warning:
    drivers/scsi/qla2xxx/qla_iocb.c:3075 qla24xx_els_dcmd2_iocb()
    warn: '&ha->plogi_els_payld.fl_csp' sometimes too small '16' size = 112

Clang warning:
    include/linux/fortify-string.h:592:4: error: call to
    '__read_overflow2_field' declared with 'warning' attribute: detected
    read beyond size of field (2nd parameter); maybe use struct_group()?
    [-Werror,-Wattribute-warning]
                        __read_overflow2_field(q_size_field, size);

When I was reading this code I assumed the "- 4" meant that we were
skipping the last 4 bytes but actually it turned out that we are
skipping the first four bytes.

I have re-written it remove the magic numbers, be more clear and
silence the static checker warnings.

Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/4aa0485e-766f-4b02-8d5d-c6781ea8f511@moroto.mountain
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Author: Dan Carpenter

drivers/scsi/qla2xxx/qla_def.h

@@ -4461,7 +4461,6 @@ struct qla_hw_data {
 
 	/* n2n */
 	struct fc_els_flogi plogi_els_payld;
-#define LOGIN_TEMPLATE_SIZE (sizeof(struct fc_els_flogi) - 4)
 
 	void            *swl;
 

drivers/scsi/qla2xxx/qla_iocb.c

@@ -3073,7 +3073,8 @@ qla24xx_els_dcmd2_iocb(scsi_qla_host_t *vha, int els_opcode,
 	memset(ptr, 0, sizeof(struct els_plogi_payload));
 	memset(resp_ptr, 0, sizeof(struct els_plogi_payload));
 	memcpy(elsio->u.els_plogi.els_plogi_pyld->data,
-	    &ha->plogi_els_payld.fl_csp, LOGIN_TEMPLATE_SIZE);
+	       (void *)&ha->plogi_els_payld + offsetof(struct fc_els_flogi, fl_csp),
+	       sizeof(ha->plogi_els_payld) - offsetof(struct fc_els_flogi, fl_csp));
 
 	elsio->u.els_plogi.els_cmd = els_opcode;
 	elsio->u.els_plogi.els_plogi_pyld->opcode = els_opcode;