Autotest: fix use of dangling pointer

The "data" pointer became technically dangling after line 1866 did
    copy = data;
as copy was the last reference to the original data. That made the
pointer address available to be reused by the system malloc(), which
sometimes happened, causing the unit test to fail.

Discussed-on: http://lists.qt-project.org/pipermail/development/2014-April/016588.html
Change-Id: Ifa6a27bd53a6e60392b77a6609f2d47148695211
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>

tests/auto/corelib/tools/qbytearray/tst_qbytearray.cpp

@@ -1863,7 +1863,7 @@ void tst_QByteArray::reserve()
     QCOMPARE(qba.capacity(), capacity);
     QCOMPARE(copy.capacity(), capacity);
 
-    copy = qba;
+    qba = copy;
     qba.reserve(capacity * 2);
     QCOMPARE(qba.size(), capacity);
     QCOMPARE(qba.capacity(), capacity * 2);