QHash: more robust use of qDebug()

I'm sure 'line' can't contain anything resembling a format string,
but better safe than sorry.

Change-Id: I0aa0f4a5a03d97b18d6a866c27fa721fcbe0f77b
Reviewed-by: Kai Koehne <kai.koehne@nokia.com>

src/corelib/tools/qhash.cpp

@@ -403,7 +403,7 @@ void QHashData::dump()
                 }
                 n = n->next;
             }
-            qDebug(qPrintable(line));
+            qDebug("%s", qPrintable(line));
         }
     }
 }