msm: clock: Return error upon invalid call to clk_set_rate

Calls to clk_set_rate should only change the voltage vote if the clock
is prepared. However, they need to check if the rate is valid even if
the clock is not prepared.

Change-Id: I5f13807e803689489f2b43bd58fbd8f46137c0e2
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>