fix typo in getLdapAttrN (#11898)

pkg/login/ldap.go

@@ -349,7 +349,7 @@ func (a *ldapAuther) searchForUser(username string) (*LdapUserInfo, error) {
 
 func getLdapAttrN(name string, result *ldap.SearchResult, n int) string {
 	if name == "DN" {
-		return result.Entries[0].DN
+		return result.Entries[n].DN
 	}
 	for _, attr := range result.Entries[n].Attributes {
 		if attr.Name == name {