Refactoring RbacUtils part 3 - documentation

Change the documnentation according to new RbacUtilsMixin

Story: 2002604
Task: 22223

Change-Id: I30ab8ea002f9312a5b50e2f2c511ed321a679c00
diff --git a/patrole_tempest_plugin/rbac_rule_validation.py b/patrole_tempest_plugin/rbac_rule_validation.py
index 95bf36a..288ec29 100644
--- a/patrole_tempest_plugin/rbac_rule_validation.py
+++ b/patrole_tempest_plugin/rbac_rule_validation.py
@@ -461,7 +461,7 @@
 
 
 def _validate_override_role_called(test_obj, actual_exception):
-    """Validates that :func:`rbac_utils.RbacUtils.override_role` is called
+    """Validates that :func:`rbac_utils.RbacUtilsMixin.override_role` is called
     during each Patrole test.
 
     Useful for validating that the expected exception isn't raised too early