Add an empty clocksource_of_init when !CLKSRC_OF. This is needed for builds
where no timer has selected CLKSRC_OF.
Signed-off-by: NRob Herring <rob.herring@calxeda.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>