msm: clock-8960: Vote for sfab @ 54Mhz in active set

The debug timer inside the Krait subsystem requires the Krait AHB
to be running at least 4 times as fast as the timer itself. The
timer runs at 27Mhz/4 and the Krait AHB runs at sfab / 2. To
ensure at least 27MHz on the Krait AHB we must force the floor of
sfab to be 54Mhz so that the Krait AHB clock never drops below
27Mhz while the timer is running.

Change-Id: I63eb1dbf26b56c7b98506fffa749e33e8991e76e
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>