QmlJS: Fix grammar file

Do not reintroduce clang warnings when regenerating code from
the grammar file.

Change-Id: Ic065191b93e68d88792fedac9784e4fbeff08d6f
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>

src/libs/qmljs/parser/qmljs.g

@@ -313,7 +313,7 @@ public:
     inline DiagnosticMessage diagnosticMessage() const
     {
         foreach (const DiagnosticMessage &d, diagnostic_messages) {
-            if (! d.kind == DiagnosticMessage::Warning)
+            if (d.kind != DiagnosticMessage::Warning)
                 return d;
         }