tests: ptimer: Change the copyright comment

Eric Blake suggested that use of "Author:" in the copyright text of the
files created by individuals is incorrect, replace it with "Copyright".

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Message-id: 9d8b626f462d4a5094b1945fbd763b8a2e28dd86.1475421224.git.digetx@gmail.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

tests/ptimer-test-stubs.c

 /*
  * Stubs for the ptimer-test
  *
- * Author: Dmitry Osipenko <digetx@gmail.com>
+ * Copyright (c) 2016 Dmitry Osipenko <digetx@gmail.com>
  *
  * This work is licensed under the terms of the GNU GPL, version 2 or later.
  * See the COPYING file in the top-level directory.

tests/ptimer-test.c

 /*
  * QTest testcase for the ptimer
  *
- * Author: Dmitry Osipenko <digetx@gmail.com>
+ * Copyright (c) 2016 Dmitry Osipenko <digetx@gmail.com>
  *
  * This work is licensed under the terms of the GNU GPL, version 2 or later.
  * See the COPYING file in the top-level directory.

tests/ptimer-test.h

 /*
  * QTest testcase for the ptimer
  *
- * Author: Dmitry Osipenko <digetx@gmail.com>
+ * Copyright (c) 2016 Dmitry Osipenko <digetx@gmail.com>
  *
  * This work is licensed under the terms of the GNU GPL, version 2 or later.
  * See the COPYING file in the top-level directory.