Doc: correct name of file with snippet

Snippet not showing because qdoc read wrong snippet file.
Due to 2 files having the same name.
One was renamed: rsslisting.cpp --> listing.cpp

Task-number: QTBUG-29101
Change-Id: I62b7eee6f2860613ee90538d8dea006b89000317
Reviewed-by: Venugopal Shivashankar <venugopal.shivashankar@digia.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>

src/xml/sax/qxml.cpp

@@ -2365,7 +2365,7 @@ events are reported.
     it we can use the same handler for both of the following
     reader functions:
 
-    \snippet rsslisting/rsslisting.cpp 0
+    \snippet rsslisting/listing.cpp 0
 
     Since the reader will inform the handler of parsing errors, it is
     necessary to reimplement QXmlErrorHandler::fatalError() if, for