copyright: remove IBM copyright

According to https://wiki.linaro.org/Copyright, all work done by assignees is
copyrighted to Linaro.
diff --git a/clocks.h b/clocks.h
index b893efc..e2be430 100644
--- a/clocks.h
+++ b/clocks.h
@@ -1,6 +1,5 @@
 /*******************************************************************************
- * Copyright (C) 2010, Linaro
- * Copyright (C) 2010, IBM Corporation
+ * Copyright (C) 2010, Linaro Limited.
  *
  * This file is part of PowerDebug.
  *