tspp: Set TSIF reference clock rate

The TSIF reference clock supports a single rate.
Set TSIF reference clock rate in the driver instead of relying
on the rate to be set externally.

Change-Id: Ie9053d116beab1c29bc2513a1fdea3ab141c2996
Signed-off-by: Liron Kuch <lkuch@codeaurora.org>