net/smc: use an array to check fields in system EID

The check for old hardware versions that did not have SMCDv2 support was
using suspicious pointer magic. Address the fields using an array.
Signed-off-by: NKarsten Graul <kgraul@linux.ibm.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/smc/smc_ism.c

@@ -335,7 +335,7 @@ int smcd_register_dev(struct smcd_dev *smcd)
 		u8 *system_eid = NULL;
 
 		smc_ism_get_system_eid(smcd, &system_eid);
-		if ((*system_eid) + 24 != '0' || (*system_eid) + 28 != '0')
+		if (system_eid[24] != '0' || system_eid[28] != '0')
 			smc_ism_v2_capable = true;
 	}
 	/* sort list: devices without pnetid before devices with pnetid */