msm_fb: display: fix mdp clk rate settings

If the video resolution is changed from higher to lower, mdp clk rate
cannot be changed before overlay_play. Otherwise, underrun may happen
because of a lower mdp clk rate for current higher resolution
frames. On the other hand, if the res is changed from lower to higher,
mdp clk rate must be changed before overlay_play to avoid underrun.

CRs-fixed: 327811
Change-Id: Ieac4d2e1644e5687e3506b37799c56e19a17b991
Signed-off-by: Huaibin Yang <huaibiny@codeaurora.org>