OAuthWebFilter: Fix 'parameter should not be assigned' warning

Don't assign a new value to the parameter that was passed
into the method.  Use the locally created copy.

Change-Id: I3a4c8ff3da6f3d0adf45cf77794459dd67595525

github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/OAuthWebFilter.java

diff --git a/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/OAuthWebFilter.java b/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/OAuthWebFilter.java
index cde4fbf..2c2afb2 100644
--- a/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/OAuthWebFilter.java
+++ b/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/OAuthWebFilter.java
@@ -89,7 +89,8 @@
         login(request, httpRequest, httpResponse, ghLogin);
       } else {
         if (OAuthProtocol.isOAuthLogout(httpRequest)) {
-          response = logout(request, response, chain, httpRequest);
+          httpResponse =
+              (HttpServletResponse) logout(request, httpResponse, chain, httpRequest);
         }
 
         if (ghLogin != null && ghLogin.isLoggedIn()) {
@@ -99,7 +100,7 @@
                   GITHUB_EXT_ID + ghLogin.getToken().accessToken);
         }
 
-        chain.doFilter(httpRequest, response);
+        chain.doFilter(httpRequest, httpResponse);
       }
     } finally {
       HttpSession httpSession = httpRequest.getSession();