s390/sthyi: Fix machine name validity indication

When running as a level 3 guest with no host provided sthyi support
sclp_ocf_cpc_name_copy() will only return zeroes. Zeroes are not a
valid group name, so let's not indicate that the group name field is
valid.

Also the group name is not dependent on stsi, let's not return based
on stsi before setting it.

Fixes: 95ca2cb5 ("KVM: s390: Add sthyi emulation")
Signed-off-by: NJanosch Frank <frankja@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/sthyi.c

@@ -183,17 +183,19 @@ static void fill_hdr(struct sthyi_sctns *sctns)
 static void fill_stsi_mac(struct sthyi_sctns *sctns,
 			  struct sysinfo_1_1_1 *sysinfo)
 {
+	sclp_ocf_cpc_name_copy(sctns->mac.infmname);
+	if (*(u64 *)sctns->mac.infmname != 0)
+		sctns->mac.infmval1 |= MAC_NAME_VLD;
+
 	if (stsi(sysinfo, 1, 1, 1))
 		return;
 
-	sclp_ocf_cpc_name_copy(sctns->mac.infmname);
-
 	memcpy(sctns->mac.infmtype, sysinfo->type, sizeof(sctns->mac.infmtype));
 	memcpy(sctns->mac.infmmanu, sysinfo->manufacturer, sizeof(sctns->mac.infmmanu));
 	memcpy(sctns->mac.infmpman, sysinfo->plant, sizeof(sctns->mac.infmpman));
 	memcpy(sctns->mac.infmseq, sysinfo->sequence, sizeof(sctns->mac.infmseq));
 
-	sctns->mac.infmval1 |= MAC_ID_VLD | MAC_NAME_VLD;
+	sctns->mac.infmval1 |= MAC_ID_VLD;
 }
 
 static void fill_stsi_par(struct sthyi_sctns *sctns,