Fix a case for DescribedClass cop

If a local variable was part of the described class's namespace, the cop
was failing.

fixes rubocop#790

lib/rubocop/cop/rspec/described_class.rb

@@ -166,7 +166,7 @@ def const_name(node)
           # rubocop:enable InternalAffairs/NodeDestructuring
           if !namespace
             [name]
-          elsif namespace.cbase_type?
+          elsif namespace.lvar_type? || namespace.cbase_type?
             [nil, name]
           else
             [*const_name(namespace), name]

spec/rubocop/cop/rspec/described_class_spec.rb

@@ -255,6 +255,18 @@ module D
         end
       RUBY
     end
+
+    it 'ignores if a local variable is part of the namespace' do
+      expect_no_offenses(<<-RUBY)
+        describe Broken do
+          [Foo, Bar].each do |klass|
+            describe klass::Baz.name do
+              it { }
+            end
+          end
+        end
+      RUBY
+    end
   end
 
   context 'when EnforcedStyle is :explicit' do