selftests: media_tests: Add SPDX license identifier

Replace GPL license statement with SPDX GPL-2.0 license identifier.
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>

tools/testing/selftests/media_tests/media_device_open.c

+// SPDX-License-Identifier: GPL-2.0
+
 /*
  * media_device_open.c - Media Controller Device Open Test
  *
  * Copyright (c) 2016 Shuah Khan <shuahkh@osg.samsung.com>
  * Copyright (c) 2016 Samsung Electronics Co., Ltd.
  *
- * This file is released under the GPLv2.
  */
 
 /*

tools/testing/selftests/media_tests/media_device_test.c

+// SPDX-License-Identifier: GPL-2.0
+
 /*
  * media_device_test.c - Media Controller Device ioctl loop Test
  *
  * Copyright (c) 2016 Shuah Khan <shuahkh@osg.samsung.com>
  * Copyright (c) 2016 Samsung Electronics Co., Ltd.
  *
- * This file is released under the GPLv2.
  */
 
 /*

tools/testing/selftests/media_tests/video_device_test.c

+// SPDX-License-Identifier: GPL-2.0
+
 /*
  * video_device_test - Video Device Test
  *
  * Copyright (c) 2016 Shuah Khan <shuahkh@osg.samsung.com>
  * Copyright (c) 2016 Samsung Electronics Co., Ltd.
  *
- * This file is released under the GPLv2.
  */
 
 /*