Add -Wextra-semi.

The headers fail to compile when included
in libhidl, because libhidl has -Wextra-semi.
I decided to clean them up and add -Wextra-semi
for all files for libvintf.

Test: builds
Change-Id: Ida1ed6d3855e582a5c09bc60128dd8c4cfd4210a
diff --git a/parse_xml.cpp b/parse_xml.cpp
index 8ccf9b1..fbac04e 100644
--- a/parse_xml.cpp
+++ b/parse_xml.cpp
@@ -393,8 +393,9 @@
     virtual bool buildObject(Object* object, NodeType* root, std::string* error) const override {
         return this->parseText(root, object, error);
     }
-    virtual std::string elementName() const { return mElementName; };
-private:
+    virtual std::string elementName() const { return mElementName; }
+
+   private:
     std::string mElementName;
 };