Fix responses to PURGE MS

When performing PURGE MS, OsmoHLR before this patch used toreturn
an error even in the successful case.  The reasone for this is some
wrong assumptions about the return values of db_subscr_purge().

Change-Id: Ie3005e2eeb424715fd77f202e9fe18464ba211b7
diff --git a/src/hlr.c b/src/hlr.c
index f3a6864..838b1bc 100644
--- a/src/hlr.c
+++ b/src/hlr.c
@@ -238,9 +238,9 @@
 	/* Perform the actual update of the DB */
 	rc = db_subscr_purge(g_hlr->dbc, gsup->imsi, true, is_ps);
 
-	if (rc == 1)
+	if (rc == 0)
 		gsup_reply.message_type = OSMO_GSUP_MSGT_PURGE_MS_RESULT;
-	else if (rc == 0) {
+	else if (rc == -ENOENT) {
 		gsup_reply.message_type = OSMO_GSUP_MSGT_PURGE_MS_ERROR;
 		gsup_reply.cause = GMM_CAUSE_IMSI_UNKNOWN;
 	} else {