msm: clock-8226: Set the mmssnoc_ahb_clk rate in post_init

The rpm expects that a message to enable clock scaling is sent prior to
any clock requests. In addition, clk_set_rate calls on rpm clocks will not
change the rate unless clk_prepare has already been called.

Change-Id: I53d0244a4858d96af6f58725b6e475a023dfa6e7
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>