[S390] memory hotplug: only unassign assigned increments

Make sure that only assigned storage increments are unassigned when
attaching a storage element.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/char/sclp_cmd.c

@@ -383,8 +383,10 @@ static int sclp_attach_storage(u8 id)
 	switch (sccb->header.response_code) {
 	case 0x0020:
 		set_bit(id, sclp_storage_ids);
-		for (i = 0; i < sccb->assigned; i++)
-			sclp_unassign_storage(sccb->entries[i] >> 16);
+		for (i = 0; i < sccb->assigned; i++) {
+			if (sccb->entries[i])
+				sclp_unassign_storage(sccb->entries[i] >> 16);
+		}
 		break;
 	default:
 		rc = -EIO;