Bugfix: == vs = mixup.

Upstream bug:
https://sourceforge.net/tracker/?func=detail&aid=3307460&group_id=146814&atid=766244

Change-Id: Idf58d7e58c1db6f9740dd44eafa69ef4e6a43e36
diff --git a/stlport/stl/_fstream.c b/stlport/stl/_fstream.c
index f1548ae..7306f9e 100644
--- a/stlport/stl/_fstream.c
+++ b/stlport/stl/_fstream.c
@@ -84,7 +84,7 @@
   if (_M_in_output_mode) {
     __ok = __ok && !_Traits::eq_int_type(this->overflow(traits_type::eof()),
                                          traits_type::eof());
-    __ok == __ok && this->_M_unshift();
+    __ok = __ok && this->_M_unshift();
   }
   else if (_M_in_input_mode)
       this->_M_exit_input_mode();