fix a typo in code

Change-Id: I19215471e54fd45a66af95f092ed88195dd5931a
diff --git a/ironic_tempest_plugin/tests/api/admin/test_nodestates.py b/ironic_tempest_plugin/tests/api/admin/test_nodestates.py
index f2a33eb..f184b8b 100644
--- a/ironic_tempest_plugin/tests/api/admin/test_nodestates.py
+++ b/ironic_tempest_plugin/tests/api/admin/test_nodestates.py
@@ -21,7 +21,7 @@
 
 
 class TestNodeStatesMixin(object):
-    """Mixin for for baremetal node states tests."""
+    """Mixin for baremetal node states tests."""
 
     @classmethod
     def resource_setup(cls):