clk: Disable writable debugfs files

[MichaIng]

Revert commit 861a024 which may be safe for Android, but is not safe for Linux and leads to a prominent warning at boot:

********************************************************************
**     NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE           **
**                                                                **
**  WRITEABLE clk DebugFS SUPPORT HAS BEEN ENABLED IN THIS KERNEL **
**                                                                **
** This means that this kernel is built to expose clk operations  **
** such as parent or rate setting, enabling, disabling, etc.      **
** to userspace, which may compromise security on your system.    **
**                                                                **
** If you see this message and you are not debugging the          **
** kernel, report this immediately to your vendor!                **
**                                                                **
**     NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE           **
********************************************************************

Also, the flag is meant for testing and debugging (Android), not for end user kernel builds.